Magnetic disk drive

Abstract

To provide a magnetic disk device capable of predicting whether error correction to a data track of a disk reaches a limit or not.SOLUTION: A magnetic disk device 1 includes a first disk having a first data track and a second data track, a first write head, a write processing unit, an error correction unit, a correction limit prediction unit 65, and a determination unit. During the write period, the correction limit prediction unit 65 calculates the excess amount OVR, calculates the metric value Mer by multiplying the excess amount OVR by the first weighting factor, updates the cumulative metric value ME, and generates the first prediction information. The determination unit determines whether to cause the write processing unit to continue the write processing on the second data track based on the first prediction information.SELECTED DRAWING: Figure 18

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a magnetic disk drive. [Background technology]

[0002] Known magnetic disk devices include conventional magnetic recording (CMR) type (or conventional recording type) magnetic disk devices that write multiple tracks spaced apart in the radial direction of the disk, shingled magnetic recording (SMR) type magnetic disk devices that overwrite multiple tracks in the radial direction of the disk, and hybrid recording type magnetic disk devices that can select between conventional recording type and shingled recording type. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-119547 [Patent Document 2] U.S. Patent No. 10,748,567 [Patent Document 3] US Patent Application Publication No. 2023 / 0260540 [Patent Document 4] U.S. Patent No. 1,091,0013 Summary of the Invention [Problem to be solved by the invention]

[0004] This embodiment provides a magnetic disk drive that can predict whether error correction for a data track on the disk will reach its limit. [Means for solving the problem]

[0005] A magnetic disk device according to an embodiment includes: a first disk having a first data track and a second data track adjacent to each other on a first recording layer, the first data track and the second data track each including a plurality of target sectors to which data is written, the first data track being positioned in a first direction parallel to a radial direction of the first disk as viewed from the second data track; a first write head that writes data to the first recording layer of the first disk; a write processing unit capable of executing a write process for writing data to the first recording layer; an error correction unit that performs error correction on data in one or more damaged target sectors determined to have damaged data among the plurality of target sectors of the first data track; a correction limit prediction unit; a determination unit, During a write period in which the write process is performed on the plurality of target sectors of the first data track and then the write process is performed on the plurality of target sectors of the second data track, The correction limit prediction unit calculating an excess amount by which the position of the first write head protrudes from a first reference radial position in the first direction every time data is written to the target sector of each of the second data tracks; calculating a metric value by multiplying the excess amount by a first weighting coefficient, which is a variable whose value changes depending on the excess amount, every time the position of the first write head exceeds the first reference radial position; updating a cumulative metric value that is a cumulative total of the metric values ​​during the write period; generating first prediction information that predicts whether the error correction for the first data track will reach a limit based on the cumulative metric value before the write process for all target sectors of the second data track is completed; The determination unit determines whether to allow the write processing unit to continue the write process on the second data track based on the first prediction information. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a block diagram showing the configuration of a magnetic disk device according to the first embodiment. [Figure 2] FIG. 2 is a perspective view showing a part of the magnetic disk device, showing a plurality of disks and a plurality of heads. [Figure 3] FIG. 3 is a schematic diagram showing an example of the arrangement of a plurality of servo areas and a plurality of data areas on one disk according to the embodiment. [Figure 4] FIG. 4 is a schematic diagram showing three tracks in the user data area of ​​the disk shown in FIG. 3 where shingled recording is performed, and a write head. [Figure 5] FIG. 5 is a schematic diagram showing three tracks of the media cache where normal recording processing of the disc shown in FIG. 3 is performed, and the write head. [Figure 6] FIG. 6 is a schematic diagram showing an example of a data write process on a disk. [Figure 7] FIG. 7 is a schematic diagram showing two bands and one guard band in the user data area shown in FIG. [Figure 8] FIG. 8 is a schematic diagram showing three sectors in one track of the band shown in FIG. [Figure 9] FIG. 9 is a schematic diagram showing the two bands and one guard band shown in FIG. 7, and is a diagram for explaining a plurality of target sectors and a plurality of unused sectors. [Figure 10] Figure 10 is a schematic diagram showing an example of the first track and the second track when it is assumed that the magnetic disk device does not have the function of performing error correction on track data on a track-by-track basis, a diagram for explaining the write process on the first track and the second track, a diagram for explaining the state in which the write process on the second track is continued until the sector-by-sector error correction on the first track reaches its limit, and a diagram showing graphs of the change in BER for the first track and the change in BER with respect to the positioning error. [Figure 11] Figure 11 is a schematic diagram showing an example of the first track and the second track when it is assumed that the magnetic disk device does not have the function of performing track-by-track error correction on track data, a diagram for explaining the write processing for the first track and the second track, a diagram for explaining the state in which the judgment value is set to a write-off track slice that is smaller (stricter) than the track margin, and the write processing for the second track is terminated when it is detected that the positioning error has become equal to or greater than the write-off track slice, and a diagram showing graphs of the change in BER for the first track and the change in BER relative to the positioning error. [Figure 12] Figure 12 is a schematic diagram showing an example of the first track and second track of the above-mentioned magnetic disk device having the function of performing track-by-track error correction on track data, a diagram for explaining the write processing on the first track and the second track, a diagram for explaining a state in which the judgment value is set to a write-off track slice that is larger (loose) than the track margin, and the write processing on the second track is continued until the track-by-track error correction on the first track reaches its limit, and a diagram showing graphs of the change in BER for the first track and the change in BER with respect to the positioning error. [Figure 13] FIG. 13 is a schematic diagram showing an example of a change in track ECC gain with respect to the number of squeezes. [Figure 14] FIG. 14 is a block diagram showing an example of a head positioning control system and a correction limit prediction unit. [Figure 15] FIG. 15 is a graph illustrating an example of the change in the number of damage target sectors in the first track versus the number of the same upper limit excess amounts and the change in the cumulative upper limit threshold. [Figure 16] FIG. 16 is a graph illustrating the cumulative number of sectors to be damaged in the first track and the excess amount of each sector to be damaged. [Figure 17]FIG. 17 is a graph illustrating the change in the cumulative metric value with respect to the number of damage target sectors in the first track, and also shows a graph illustrating the change in the cumulative upper limit threshold shown in FIG. [Figure 18] FIG. 18 is a block diagram showing an example of a head positioning control system and a correction limit prediction unit according to the embodiment. [Figure 19] FIG. 19 is a graph showing the change in the first weighting coefficient with respect to the excess amount. [Figure 20] FIG. 20 is a graph illustrating an example of the change in the average metric value with respect to the number of sectors to be damaged. [Figure 21] FIG. 21 is a graph illustrating an example of the change in the upper limit of the cumulative metric value with respect to the number of sectors to be damaged. [Figure 22] FIG. 22 is a graph illustrating the cumulative number of damaged sectors in the first track and the individual metric values. [Figure 23] FIG. 23 is a graph illustrating the change in the cumulative metric value with respect to the number of damage target sectors in the first track, and also shows a graph in which the cumulative upper limit threshold shown in FIG. 21 is constant. [Figure 24] Figure 24 is a schematic diagram showing an example of the third track and fourth track of a magnetic disk device according to the second embodiment, a diagram for explaining the write processing for the third track and the fourth track, a diagram for explaining a state in which the judgment value is set to a write-off track slice that is larger (loose) than the track margin, and the write processing for the fourth track is continued until the track-by-track error correction for the third track reaches its limit, and a diagram showing graphs of the change in BER for the third track and the change in BER relative to the positioning error. DETAILED DESCRIPTION OF THE INVENTION

[0007] (First embodiment) A magnetic disk device 1 according to a first embodiment will be described in detail below with reference to the drawings. First, the configuration of the magnetic disk device 1 will be described. FIG. 1 is a block diagram showing the configuration of the magnetic disk device 1 according to the first embodiment. In this embodiment, the magnetic disk device 1 is a hybrid recording type magnetic disk device that selectively executes a normal recording type and a shingled recording type. However, the techniques described below may be applied to a shingled recording type magnetic disk device or a normal recording type magnetic disk device.

[0008] 1, the magnetic disk device 1 includes a plurality of, for example, 1 to 10 disks (magnetic disks) DK as recording media, a spindle motor (SPM) 20 as a drive motor, a head stack assembly 22, a driver IC 120, a head amplifier integrated circuit (hereinafter referred to as head amplifier IC or preamplifier) ​​130, a volatile memory 70, a buffer memory (buffer) 80, a nonvolatile memory 90, and a system controller 110 which is a one-chip integrated circuit. The magnetic disk device 1 is also connected to a host system (hereinafter simply referred to as host) 100.

[0009] Each disk DK is formed to have a diameter of, for example, 97 mm (3.8 inches) and has a recording layer (magnetic recording layer) on both sides. In the first embodiment, the magnetic disk device 1 is equipped with 1 to 11 disks DK, but the number of disks DK is not limited to these.

[0010] The head stack assembly 22 can control the movement of the head HD mounted on the arm 30 to a target position on the disk DK, i.e., can seek, by driving the voice coil motor (hereinafter referred to as VCM) 24. The VCM 24 functions as an actuator. The disk DK has a user data area U that can be used by the user and a system area S in which information required for system management is written, as areas where data can be written.

[0011] The head HD records and reproduces information on the disk DK. The head HD has a slider as its main body, and is equipped with a write head WHD and a read head RHD mounted on the slider. The write head WHD writes data to the recording layer of the disk DK. The read head RHD reads data from the data tracks on the recording layer of the disk DK.

[0012] The "center of the head HD" may be referred to as the "head HD", the "center of the write head WHD" may be referred to as the "write head WHD", and the "center of the read head RHD" may be referred to as the "read head RHD". The "center of the write head WHD" may be simply referred to as the "head HD", and the "center of the read head RHD" may be simply referred to as the "head HD".

[0013] The driver IC 120, under the control of the system controller 110 (more specifically, the MPU 60 described later), controls the driving of the SPM 20 and VCM 24. The SPM 20 supports and rotates a plurality of discs DK.

[0014] The head amplifier IC 130 includes a read amplifier and a write driver. The read amplifier amplifies a read signal read from the disk DK and outputs it to the system controller 110 (more specifically, to a read / write (R / W) channel 140, which will be described later). The write driver outputs a write current to the head HD according to the signal output from the R / W channel 140.

[0015] The volatile memory 70 is a semiconductor memory in which stored data is lost when the power supply is cut off. The volatile memory 70 stores data and the like required for processing in each section of the magnetic disk device 1. The volatile memory 70 is a random access memory (RAM). The volatile memory 70 is, for example, a dynamic random access memory (DRAM). However, the volatile memory 70 may also be a synchronous dynamic random access memory (SDRAM).

[0016] The buffer memory 80 is a semiconductor memory that temporarily records data and the like transmitted and received between the magnetic disk device 1 and the host 100. The buffer memory 80 may be configured integrally with the volatile memory 70. The buffer memory 80 is a volatile RAM. For example, the buffer memory 80 is a DRAM, an SRAM (Static Random Access Memory), an SDRAM, an FeRAM (Ferroelectric Random Access Memory), an MRAM (Magnetoresistive Random Access Memory), or the like. The buffer memory 80 includes areas used as a read cache and a write cache, and temporarily stores commands received from the host 100 .

[0017] The nonvolatile memory 90 is a semiconductor memory that records stored data even when the power supply is cut off. The nonvolatile memory 90 is, for example, a NAND-type flash read only memory (FROM). However, the nonvolatile memory 90 may also be a NOR-type FROM.

[0018] The system controller (controller) 110 is realized, for example, using a large-scale integrated circuit (LSI) called a system-on-a-chip (SoC), in which multiple elements are integrated on a single chip. The system controller 110 includes a read / write (R / W) channel 140, a hard disk controller (HDC) 150, and a microprocessor (MPU) 60. The system controller 110 is electrically connected to a driver IC 120, a head amplifier IC 130, a volatile memory 70, a buffer memory 80, a non-volatile memory 90, and a host 100.

[0019] The R / W channel 140 performs signal processing of read data transferred from the disk DK to the host 100 and write data transferred from the host 100 in response to instructions from the MPU 60 (described later). The R / W channel 140 has a circuit or function for modulating write data. The R / W channel 140 also has a circuit or function for measuring the signal quality of the read data. The R / W channel 140 is electrically connected to, for example, the head amplifier IC 130, the HDC 150, the MPU 60, etc.

[0020] The HDC 150 controls data transfer between the host 100 and the R / W channel 140 in response to instructions from the MPU 60, which will be described later. The HDC 150 is electrically connected to, for example, the R / W channel 140, the MPU 60, the volatile memory 70, the buffer memory 80, the non-volatile memory 90, and the like.

[0021] The HDC 150 has a gate generation unit. The gate generation unit generates various gates, such as write gates, read gates, and servo gates, in response to commands from the host 100 and instructions from the MPU 60, and outputs them to the R / W channel 140, for example, to a gate detection unit. Hereinafter, "raising a specified gate" may also be referred to as "asserting a specified gate." Also, "lowering a specified gate" may also be referred to as "negating a specified gate." "Asserting a specified gate" or "negating a specified gate" may also include the meaning of "generating a specified gate." The gate generation unit may be included in the R / W channel 140 or the MPU 60.

[0022] The R / W channel 140 has a gate detection unit that detects whether various gates, such as a write gate, a read gate, and a servo gate, are in an asserted state or a negated state. For example, the gate detection unit executes the write process when it detects that the write gate is asserted, and pauses (stops) the write process when it detects that the write gate is negated. In addition, the gate detector executes a read process when it detects that the read gate is asserted, and stops the read process when it detects that the read gate is negated. The gate detector executes a servo read process when it detects that the servo gate is asserted, and stops the servo read process when it detects that the servo gate is negated. The gate detector may be located within the HDC 150 or the MPU 60.

[0023] The MPU 60 is a control unit and a main controller that controls each unit of the magnetic disk device 1. The MPU 60 controls the VCM 24 via the driver IC 120 and executes servo control to position the head HD. The MPU 60 controls the operation of writing data to the disk DK and selects a destination for write data transferred from the host 100. The MPU 60 also controls the operation of reading data from the disk DK and controls the processing of read data transferred from the disk DK to the host 100. The MPU 60 is connected to each unit of the magnetic disk device 1. The MPU 60 is electrically connected to, for example, the driver IC 120, the R / W channel 140, the HDC 150, etc.

[0024] The MPU 60 includes a read / write processing unit 61, an error correction unit 64, a correction limit prediction unit 65, a judgment unit 66, a switching unit 67, etc. The MPU 60 executes the processing of each of these units, for example, the read / write processing unit 61, the error correction unit 64, the correction limit prediction unit 65, the judgment unit 66, the switching unit 67, etc., on firmware. Note that the MPU 60 may include each of these units as a circuit.

[0025] The read / write processing unit 61 has a write processing unit 62 and a read processing unit 63. In accordance with commands from the host 100, the write processing unit 62 controls data write processing, and the read processing unit 63 controls data read processing, causing the read head RHD to read data from the disk DK. The write processing unit 62 can execute write processing to write data to the recording layer of the disk DK. The read / write processing unit 61 controls the VCM 24 via the driver IC 120, positions the head HD to a target position (predetermined radial position) on the disk DK, and executes read processing or write processing.

[0026] FIG. 2 is a perspective view showing a part of the magnetic disk device 1, and shows a plurality of disks DK and a plurality of heads HD. As shown in Fig. 2, the direction in which the disk DK rotates in the circumferential direction is referred to as the rotation direction d3. Note that in the example shown in Fig. 2, the rotation direction d3 is shown counterclockwise, but it may be the opposite direction (clockwise). Also, the movement direction d2 of the head HD relative to the disk DK is opposite to the rotation direction d3. The movement direction d2 is the direction in which the head HD sequentially writes and reads data to and from the disk DK in the circumferential direction, that is, the direction in which the head HD moves relative to the disk DK in the circumferential direction.

[0027] The magnetic disk device 1 includes i disks, disks DK1 to DKi, and j heads, heads HD1 to HDj. In this embodiment, the number of heads HD is twice the number of disks DK (j=2×i). The disks DK1 to DKi are arranged coaxially and stacked with a gap between them. The disks DK1 to DKi have the same diameter. Here, terms such as "same," "identical," "matched," and "equivalent" not only mean exactly the same, but also mean different enough to be considered substantially the same. The diameters of the disks DK1 to DKi may be different from each other.

[0028] Each disc DK has recording layers L on both sides. For example, disc DK1 has a first recording layer La1 and a second recording layer Lb1 opposite the first recording layer La1. Disc DK2 has a first recording layer La2 and a second recording layer Lb2 opposite the first recording layer La2. Disc DKi has a first recording layer Lai and a second recording layer Lbi opposite the first recording layer Lai. Each first recording layer La may also be referred to as a front surface or recording surface. Each second recording layer Lb may also be referred to as a back surface or recording surface. However, each first recording layer La may also be referred to as the back side, and in this case, each second recording layer Lb may also be referred to as the front side.

[0029] Each recording layer L has a user data area U and a system area S. The first recording layer La1 has a user data area Ua1 and a system area Sa1. The second recording layer Lb1 has a user data area Ub1 and a system area Sb1. The first recording layer La2 has a user data area Ua2 and a system area Sa2. The second recording layer Lb2 has a user data area Ub2 and a system area Sb2. The first recording layer Lai has a user data area Uai and a system area Sai. The second recording layer Lbi has a user data area Ubi and a system area Sbi.

[0030] In the user data area Ua1 (first recording layer La1), the track sandwiched between the double dashed lines in the figure is called track Ta1. In the user data area Ub1 (second recording layer Lb1), the track located on the opposite side of track Ta1 is called track Tb1. In the user data area Ua2 (first recording layer La2), the track sandwiched between the double dashed lines in the figure is called track Tc1, and in the user data area Ub2 (second recording layer Lb2), the track located on the opposite side of track Tc1 is called track Td1. In the user data area Uai (first recording layer Lai), the track sandwiched between the double dashed lines in the figure is called track Te1. In the user data area Ubi (second recording layer Lbi), the track located on the opposite side of track Te1 is called track Tf1. In this embodiment, the tracks Ta1, Tb1, Tc1, Td1, Te1, and Tf1 are located on the same cylinder.

[0031] The head HD faces the disk DK. In this embodiment, one head HD faces each recording layer L of the disk DK. For example, head HD1 faces the first recording layer La1 of the disk DK1, writes data to the first recording layer La1, and reads data from the first recording layer La1. Head HD2 faces the second recording layer Lb1 of the disk DK1, writes data to the second recording layer Lb1, and reads data from the second recording layer Lb1.

[0032] Head HD3 faces the first recording layer La2 of disk DK2 and writes data to and reads data from the first recording layer La2. Head HD4 faces the second recording layer Lb2 of disk DK2 and writes data to and reads data from the second recording layer Lb2. Head HDj-1 faces the first recording layer Lai of disk DKi and writes data to and reads data from the first recording layer Lai. Head HDj faces the second recording layer Lbi of disk DKi and writes data to and reads data from the second recording layer Lbi.

[0033] 3 is a schematic diagram showing an example of the arrangement of a plurality of servo areas SV and a plurality of data areas DTR on one disk DK according to the first embodiment. As shown in FIG. 3, in the radial direction d1 of the disk DK, the direction toward the outer periphery of the disk DK is referred to as the outward direction (outside), and the direction opposite to the outward direction is referred to as the inward direction (inside). In FIG. 3, the user data area U is divided into an inner area IR located inward, an outer area OR located outward, and a middle area MR located between the inner area IR and the outer area OR.

[0034] The disk DK has a plurality of servo areas SV and a plurality of data areas DTR. The plurality of servo areas SV may, for example, extend radially in the radial direction of the disk DK and be discretely arranged at predetermined intervals in the circumferential direction. The plurality of servo areas SV may, for example, extend linearly from the inner circumference to the outer circumference and be discretely arranged at predetermined intervals in the circumferential direction. The plurality of servo areas SV may, for example, extend spirally from the inner circumference to the outer circumference and be discretely arranged at predetermined intervals in the circumferential direction. Furthermore, the plurality of servo areas SV may, for example, be arranged in an island-like manner in the radial direction and be discretely arranged at predetermined intervals in the circumferential direction.

[0035] Hereinafter, one servo area SV in a given track may be referred to as a "servo sector." Note that a "servo area SV" may also be referred to as a "servo sector SV." A servo sector contains servo data. Hereinafter, "the arrangement of several servo data that make up a servo sector" may also be referred to as a "servo pattern." Note that "servo data written in a servo sector" may also be referred to as a "servo sector."

[0036] Each of the multiple data areas DTR is disposed between multiple servo areas SV. For example, a data area DTR corresponds to an area between two consecutive servo areas SV in the circumferential direction. Hereinafter, one data area DTR in a given track may be referred to as a "data sector." Note that a "data area DTR" may also be referred to as a "data sector DTR." A data sector contains user data. Note that "user data written to a data sector" may also be referred to as a "data sector." A "data sector" may also be referred to as "user data." Also, a "pattern composed of several pieces of data" may also be referred to as a "data pattern." In the example shown in FIG. 3, the data pattern of a given track is composed of multiple servo data (servo sectors) and multiple user data (data sectors).

[0037] The servo area SV has a plurality of zone servo areas ZSV, etc. In addition to the zone servo areas ZSV, the servo area SV may also include an area including a gap (a deviation in the circumferential position of two zone servo areas), an area including servo data, and a data area DTR, etc. The plurality of zone servo areas ZSV are discretely arranged along the radial direction d1. Each of the plurality of zone servo areas ZSV extends in the radial direction d1.

[0038] One zone servo area (servo area) ZSV in a specified track may be referred to as a "zone servo sector" or "servo sector." Note that a "zone servo area (servo area) ZSV" may also be referred to as a "zone servo sector ZSV" or "servo sector ZSV." "Servo data written in a zone servo sector" may also be referred to as a "zone servo sector" or "servo sector." Hereinafter, "the arrangement of several servo data constituting a zone servo sector" may also be referred to as a "zone servo pattern" or "servo pattern." Hereinafter, one servo area SV in a specified track may also be referred to as a "zone pattern sector."

[0039] Note that a "servo area SV" may also be referred to as a "zone pattern sector." "At least one piece of data, etc. written to a zone pattern sector" may also be referred to as a "zone pattern sector." A zone pattern sector includes at least one zone servo sector. Hereinafter, "data pattern of a zone pattern sector" may also be referred to as a "zone data pattern."

[0040] 3, the servo area SV has zone servo areas ZSV0, ZSV1, and ZSV2. The zone servo areas ZSV0, ZSV1, and ZSV2 are arranged in a staggered pattern in the radial direction. The zone servo areas ZSV0, ZSV1, and ZSV2 may also be arranged in a stepped pattern in the radial direction.

[0041] Zone servo area ZSV2 is located closer to the inner periphery than zone servo area ZSV1. Zone servo area ZSV0 is located closer to the outer periphery than zone servo area ZSV1. For example, zone servo area ZSV2 is arranged from inner area IR to middle area MR, zone servo area ZSV1 is arranged from inner area IR to outer area OR, and zone servo area ZSV0 is arranged from middle area MR to outer area OR. Hereinafter, in a given servo area SV, a given radial area in which multiple zone servo areas ZSV are arranged in the circumferential direction may also be referred to as a zone servo boundary area, a double servo area, or a double zone servo area ZB.

[0042] In the example shown in Fig. 3, the primary servo areas SVO and the secondary servo areas SVE are alternately arranged at intervals in the circumferential direction. For example, one secondary servo area SVE is arranged between two primary servo areas SVO that are consecutively arranged at an interval in the circumferential direction. In other words, one secondary servo area SVE is arranged between two primary servo areas SVO that are consecutively arranged at an interval in the circumferential direction. For example, if consecutive numbers are assigned to all the servo areas SV of the disk DK in order, the primary servo areas SVO correspond to the odd-numbered servo areas SV, and the secondary servo areas SVE correspond to the even-numbered servo areas SV. Note that two or more secondary servo areas SVE may be arranged between two primary servo areas SVO that are consecutively arranged at an interval in the circumferential direction.

[0043] The primary servo area SVO and the secondary servo area SVE may be, for example, composed only of a servo area (hereinafter sometimes referred to as a normal servo area) that reads and demodulates servo data as a whole. Hereinafter, "reading and demodulating servo data" may also be referred to as "servo reading." The primary servo area SVO and the secondary servo area SVE may be, for example, composed of a normal servo area and a servo area (hereinafter sometimes referred to as a short servo area) that servo reads a circumferential range of servo data that is smaller than the circumferential range of servo data servo read in the normal servo area.

[0044] The media cache M is allocated to the disk DK. However, the media cache M does not have to be located on the disk DK. By using the above-mentioned plurality of servo data, for example, it is possible to derive the positioning error of the head HD (for example, the write head WHD).

[0045] In the explanation of the first embodiment, the disk DK has three zones, but the number of zones on the disk DK can be changed in various ways. The number of zones on the disk DK may be 30 to 40. Furthermore, each zone has multiple bands. For example, each zone may have several hundred bands.

[0046] 4 is a schematic diagram showing the write head WHD and three tracks STR in the user data area U where shingled recording is performed on the disk DK shown in FIG. 3. The user data area U is a shingled recording area. Within the user data area U, it is permitted to write data sequentially in band units, that is, shingled recording is permitted.

[0047] As shown in Fig. 4, the write head WHD can sequentially write data to the disk DK in the travel direction d2. The read head RHD shown in Fig. 3 can also sequentially read data written to the disk DK in the travel direction d2.

[0048] The direction in which a plurality of tracks STR, which are a plurality of data tracks, are continuously shingled-recorded in a direction parallel to the radial direction d1, that is, the direction in which the next track STR to be written is overlapped on the track STR written one before in the radial direction d1, is called the overwrite direction or recording progress direction. In the band BAe shown in Figure 4, the overwrite direction d5 is an inward direction, but the overwrite direction may also be an outward direction. For example, the overwrite direction applied to multiple bands BA (multiple zones Z) located on the outer side of a specific radial position may be opposite to the overwrite direction applied to multiple bands BA (multiple zones Z) located on the inner side of the specific radial position.

[0049] Band BAe has a plurality of tracks STR, including tracks STRe, STRe+1, and STRe+2. Tracks STRe, STRe+1, and STRe+2 are continuously overwritten in the order shown in the overwrite direction d5. Of tracks STRe, STRe+1, and STRe+2, track STRe corresponds to the track onto which data is written first, and track STRe+2 corresponds to the track onto which data is written last.

[0050] Track STRe has a track center STCe at the center in the radial direction d1 when no other tracks have been overwritten. Track STRe+1 has a track center STCe+1 at the center in the radial direction d1 when no other tracks have been overwritten. Track STRe+2 has a track center STCe+2 at the center in the radial direction d1 when no other tracks have been overwritten.

[0051] In the example shown in Figure 4, tracks STRe, STRe+1, and STRe+2 are written at a pitch (shingled recording track pitch) STP. The track center STCe of track STRe and the track center STCe+1 of track STRe+1 are spaced apart in the radial direction d1 by a pitch STP. The track center STCe+1 of track STRe+1 and the track center STCe+2 of track STRe+2 are spaced apart in the radial direction d1 by a pitch STP. Tracks STRe to STRe+2 may be written at different pitches.

[0052] The width in the radial direction d1 of the area of ​​track STRe where track STRe+1 is not overwritten is the same as the width in the radial direction d1 of the area of ​​track STRe+1 where track STRe+2 is not overwritten. Note that the width in the radial direction d1 of the area of ​​track STRe where track STRe+1 is not overwritten may be different from the width in the radial direction d1 of the area of ​​track STRe+1 where track STRe+2 is not overwritten.

[0053] In Fig. 4, for convenience of explanation, each track STR is shown as a rectangle, but in reality, each track STR is curved along the circumferential direction. Also, each track STR may be wavy, extending in the circumferential direction while fluctuating in the radial direction d1. Note that in Fig. 4, three tracks STR are overwritten, but two tracks STR may be overwritten, or more than three tracks STR may be overwritten.

[0054] The write processing unit 62 selects a shingled recording format in which data is written to multiple tracks STR in an overwrite direction d5, and causes the write head WHD to write data to each band BA. In the example shown in Fig. 4, the write processing unit 62 sequentially shingles data on tracks STRe to STRe+2 in band BAe inward (in the overwrite direction d5) at a pitch STP. Since data is written to the user data area U using the shingled recording format, the recording density of the user data area U can be improved.

[0055] The write processing unit 62 writes track STRe+1 inward from track STRe at pitch STP, and overwrites track STRe+1 on a part of the inner circumference side of track STRe. The write processing unit 62 writes track STRe+2 inward from track STRe+1 at pitch STP, and overwrites track STRe+2 on a part of the inner circumference side of track STRe+1.

[0056] Figure 5 is a schematic diagram showing the three tracks CTR and the write head WHD of the media cache M where normal recording processing of the disk DK shown in Figure 3 is performed. The media cache M and the system area S shown in Figure 3 are normal recording areas. Random data writing is permitted in the media cache M and the system area S, that is, normal recording is permitted.

[0057] 5, the media cache M has a plurality of tracks CTR including tracks CTRe, CTRe+1, and CTRe+2. Each of the plurality of tracks CTR is a data track. For example, the width in the radial direction d1 (track width) of the tracks CTRe, CTRe+1, and CTRe+2 is the same. Note that the track widths of the tracks CTRe to CTRe+2 may be different from each other.

[0058] Track CTRe has a track center CTCe at the center in the radial direction d1, track CTRe+1 has a track center CTCe+1 at the center in the radial direction d1, and track CTRe+2 has a track center CTCe+2 at the center in the radial direction d1. In the example shown in Fig. 5, tracks CTRe, CTRe+1, and CTRe+2 are written at a pitch (normal recording track pitch) CTP. The track center CTCe of track CTRe and the track center CTCe+1 of track CTRe+1 are separated by the pitch CTP. The track center CTCe+1 of track CTRe+1 and the track center CTCe+2 of track CTRe+2 are separated by the pitch CTP.

[0059] The tracks CTRe and CTRe+1 are separated by a gap GP. The tracks CTRe+1 and CTRe+2 are separated by a gap GP. The tracks CTRe to CTRe+2 may be written at different pitches. For ease of explanation, each track CTR is shown as a rectangle in FIG. 5, but in reality, each track CTR is curved along the circumferential direction. Furthermore, each track CTR may be wavy, extending in the circumferential direction while fluctuating in the radial direction d1.

[0060] The write processing unit 62 can select a normal recording format in which data is written to a plurality of tracks CTR at intervals in the radial direction d1 of the disk DK and perform the write processing. In the example shown in Figure 5, the write processing unit 62 positions the write head WHD at the track center CTCe in a predetermined area of ​​the disk DK and performs normal recording on the track CTRe or a predetermined sector of the track CTRe.

[0061] The write processing unit 62 positions the write head WHD at a track center CTCe+1 that is spaced inward from the track center CTCe of the track CTRe by the pitch CTP, and performs normal recording on the track CTRe+1 or a predetermined sector of the track CTRe+1. The write processing unit 62 positions the write head WHD at a track center CTCe+2 that is spaced inward from the track center CTCe+1 of the track CTRe+1 by the pitch CTP, and performs normal recording on the track CTRe+2 or a predetermined sector of the track CTRe+2.

[0062] The write processing unit 62 may normally record tracks CTRe, CTRe+1, and CTRe+2 sequentially in a predetermined area of ​​the disk DK, or may normally record randomly in a predetermined sector of track CTRe, a predetermined sector of track CTRe+1, and a predetermined sector of track CTRe+2.

[0063] 6 is a schematic diagram showing an example of data write processing on a disk DK. Tracks STR and CTR are data tracks. As shown in FIG. 6, the user data area U has bands BAa, BAb, and BAc. Bands BAa, BAb, and BAc belong to the same zone Ze. In zone Ze, bands BAa, BAb, and BAc are arranged intermittently in the overwrite direction in the order in which they are written.

[0064] Bands BAa and BAb are adjacent to each other in the radial direction d1, and bands BAb and BAc are adjacent to each other in the radial direction d1. Band BAa includes x tracks: STRa0, STRa1, STRa2, ..., STRa(x-3), STRa(x-2), and STRa(x-1). Tracks STRa0 to STRa(x-1) are shingled recorded in the order listed in the overwrite direction d5. In band BAa, track STRa0 corresponds to the first track onto which data is written first, and track STRa(x-1) corresponds to the last track onto which data is written last.

[0065] Band BAb includes x tracks: STRb0, STRb1, STRb2, ..., STRb(x-3), STRb(x-2), and STRb(x-1). Tracks STRb0 to STRb(x-1) are shingled recorded in the order listed in the overwrite direction d5. In band BAb, track STRb0 corresponds to the first track onto which data is written first, and track STRb(x-1) corresponds to the last track onto which data is written last.

[0066] Band BAc includes x tracks: STRc0, STRc1, STRc2, ..., STRc(x-3), STRc(x-2), and STRc(x-1). Tracks STRc0 to STRc(x-1) are shingled recorded in the order listed in the overwrite direction d5. In band BAc, track STRc0 corresponds to the first track onto which data is written first, and track STRc(x-1) corresponds to the last track onto which data is written last.

[0067] Each band BA belonging to the same zone Z has the same number of tracks STR. For example, each band BA belonging to zone Ze has the same number of tracks STR. In other words, the number of tracks STR that a band BA has is fixed for each zone Z. In this example, the number of tracks STR that each band BA belonging to zone Ze has is x.

[0068] Fig. 6 shows tracks CTR(x-2) and CTR(x-1). In Fig. 6, tracks CTR(x-2) and CTR(x-1) are usually recorded in the media cache M or the system area S. Tracks CTR(x-2) and CTR(x-1) are adjacent to each other in the radial direction d1.

[0069] Fig. 7 is a schematic diagram showing two bands BAa and BAb and one guard band GB in the user data area U shown in Fig. 6. As shown in Fig. 7, the shingled recording method differs from the normal recording method in that part of the track STR is overwritten, and therefore the MPU 60 manages the track group in the user data area U in units called bands.

[0070] A guard band GB is generally provided between bands BA adjacent in the radial direction d1. The guard band GB includes a guard track GTR. Unlike the first embodiment, the guard band GB may include multiple guard tracks GTR. The guard band GB has the role of suppressing interference between adjacent bands BA. The guard band GB makes it possible to perform shingled recording in units of one band BA. Furthermore, the guard band GB makes it possible to separate the ranges (bands BA) to be written sequentially.

[0071] For example, the track center STCa(x-3) of track STRa(x-3), the track center STCa(x-2) of track STRa(x-2), the track center STCa(x-1) of track STRa(x-1), the track center GTC of the guard track GTR, the track center STCb0 of track STRb0, the track center STCb1 of track STRb1, and the track center STCb2 of track STRb2 are positioned at equal pitches in the overwrite direction d5.

[0072] Excluding the guard band GB, the recording capacity of each band BA in the user data area U is usually predetermined based on the user's required specifications. The MPU 60 can record the same amount of data in each band BA. Typically, the recording capacity of each band BA is 128 MiB or 256 MiB.

[0073] 8 is a schematic diagram showing three sectors SCe, SC(e+1), and SC(e+2) of one track STRa0 of band BAa shown in FIG. 6. As shown in FIG. 8, each track STR has a plurality of sectors SC. Track STRa1 has a plurality of sectors SC including sectors SCe, SC(e+1), and SC(e+2). Each track STR belonging to the same zone Z has the same number of sectors SC. In this first embodiment, each track STR belonging to zone Ze has y sectors SC.

[0074] Each sector SC has a length Ls in the circumferential direction of the disk DK. Each sector SC may be a split sector separated by a servo sector SV. In this case, the length of the sector SC does not have to be Ls. The write head WHD is a magnetic head for energy-assisted recording (EAMR) that performs energy-assisted magnetic recording. In the first embodiment, the write head WHD is configured to use energy other than magnetic energy, but the write head WHD is not limited to this and may be a magnetic head that is not configured to perform energy-assisted recording.

[0075] FIG. 9 is a schematic diagram showing the two bands BAa and BAb and one guard band GB shown in FIG. 7, and is a diagram for explaining a plurality of target sectors RSC and a plurality of unused sectors VSC. In Fig. 9, for convenience of explanation, each track STR is shown as a rectangle, but in reality, each track STR is curved along the circumferential direction. Furthermore, although multiple tracks STR are arranged in the overwrite direction d5 without overlapping, in reality, multiple tracks STR are arranged in the overwrite direction d5 while overlapping. Furthermore, in the figure, target sectors RSC are marked with a dot pattern. Unused sectors VSC are shown as plain.

[0076] As shown in Figure 9, the band number of band BAa is "a" and the band number of band BAb is "b". The track numbers of each band BA are "0" to "x-1". The sector numbers of each track STR are "0" to "y-1". Hereinafter, sector SC of each band BA may be identified using the following symbol: "SC (track number, sector number)".

[0077] In the first embodiment, band BAa is a band adjacent to band BAb, and is a band located to the right of band BAb in the overwriting direction d5. Each track STR in band BAa contains G target sectors RSC (one or more target sectors RSC) in which valid data is written. For example, track STRa0 has y target sectors RSC (G=y). All sectors SC in track STRa0 are target sectors RSC. Track STRa(x-1) has five target sectors RSC (G=5). The remaining sectors SC in track STRa(x-1) are unused sectors VSC in which valid data is not written. From the above, the number of target sectors RSC in track STRa0 is different from the number of target sectors RSC in track STRa(x-1).

[0078] In each band BA of zone Ze, all sectors SC in x-1 tracks STR numbered 0 to x-2 are target sectors RSC in which valid data is written and are recording sectors USC. In the x-1 track STR of each band BA of zone Ze, five sectors SC numbered 0 to 4 are target sectors RSC and are recording sectors USC. Meanwhile, in the x-1 track STR, the remaining sectors SC numbered 5 to y-1 are unused sectors VSC in which valid data is not written.

[0079] 10 is a schematic diagram showing an example of the first track STR0 and the second track STR1 when it is assumed that the magnetic disk device 1 does not have a function for performing error correction on the data of the track TR, a diagram for explaining the write process on the first track STR0 and the second track STR1, a diagram for explaining a state in which the write process on the second track STR1 is continued until the error correction per sector on the first track STR0 reaches its limit, and a graph showing the change in the bit error rate (BER) for the first track STR0 and the change in the BER relative to the positioning error (PE). In the explanation using FIG. 10, the magnetic disk device 1 will be described as not having the error correction unit 64 of FIG. 1. Also, in FIG. 10, for convenience of explanation, the first track STR0, etc. are drawn as if the circumferential direction is linear.

[0080] 10, the first track STR0 and the second track STR1 are data tracks, and all sectors SC of the first track STR0 and all sectors (data sectors) SC of the second track STR1 are target sectors RSC. The write process for the first track STR0 is ideally performed without a positioning error PE (PE≈0, or PE=0).

[0081] If the magnetic disk drive 1 is affected by external vibrations or the like during a write process, a positioning error PE occurs when positioning the write head WHD. The positioning error PE is the amount of deviation of the write head WHD from its target position in the radial direction d1. By setting the track margin TM, it is possible to determine the tolerance range within which it is guaranteed that data on adjacent tracks can be read.

[0082] For example, when a write operation is performed on the second track STR1, if the target sectors RSCe, RSC(e+1), and RSC(e+2) of the first track STR0 are adjacent to the write head WHD in the radial direction d1 during the period when the positioning error PE exceeds the track margin TM, the data in the target sectors RSCe, RSC(e+1), and RSC(e+2) of the first track STR0 is determined (predicted) to be corrupted. While a lower data BER is desirable, the BER of the data in the target sectors RSCe, RSC(e+1), and RSC(e+2) of the first track STR0 exceeds the threshold BERTH. As can be seen from the graph on the right side of Figure 10, the larger the positioning error PE, the greater the adverse effect of ATI (Adjacent Track Interference). The BER of the data in the first track STR0, which is excessively affected by ATI, becomes excessively high.

[0083] Therefore, among the multiple target sectors RSC in the first track STR0, target sectors RSCe, RSC(e+1), and RSC(e+2) are determined to be damage target sectors CSC1, CSC2, and CSC3, respectively, which may result in a deterioration in the quality of the signal obtained by reading the data from the damage target sectors CSC1 to CSC3, or in the erasure of the data from the damage target sectors CSC1 to CSC3.

[0084] 10, the magnetic disk device 1 does not have a function for performing track-by-track error correction on the data of the track TR. Here, the track-by-track error correction is also called track error correction, track ECC (Error Checking and Correcting), etc. Therefore, the target sector RSCe, the target sector RSC(e+1), and the target sector RSC(e+2) remain as damaged target sector CSC1, the damaged target sector CSC2, and the damaged target sector CSC3.

[0085] 10, it is assumed that all target sectors RSC of the track TR have a common track margin TM. In the explanations of Fig. 11 and Fig. 12 described later, it is also assumed that all target sectors RSC of the track TR have a common track margin TM. However, the setting of the track margin TM above is just an example, and the track margin TM may be different for each target sector RSC.

[0086] 11 is a schematic diagram showing an example of the first track STR0 and the second track STR1 when it is assumed that the magnetic disk device 1 does not have a function for performing track-by-track error correction on data in the track TR. It is also a diagram for explaining the write process for the first track STR0 and the second track STR1. It is also a diagram for explaining a state in which the judgment value is set to a write-off-track slice WOS smaller (stricter) than the track margin TM, and the write process for the second track STR1 is paused when it is detected that the positioning error PE is equal to or greater than the write-off-track slice WOS. It is also a graph showing the change in BER for the first track STR0 and the change in BER relative to the positioning error PE. For ease of explanation, the first track STR0, etc. are also depicted as being linear in the circumferential direction in FIG. 11. In the explanation using FIG. 11, the magnetic disk device 1 will be described as not including the error correction unit 64 of FIG. 1.

[0087] As shown in FIG. 11, the first track STR0 and the second track STR1 are each data tracks, and all sectors SC of the first track STR0 and all sectors (data sectors) SC of the second track STR1 are each target sectors RSC. The write process for the first track STR0 is ideally executed without a positioning error PE (PE≒0 or PE = 0).

[0088] In order to prevent or suppress the write process in a state where the positioning error PE exceeds the track margin TM, the magnetic disk device 1 has a write off-track slice WOS. During the period of writing data to the second track STR1, when it is determined that the positioning error PE exceeds the write off-track slice WOS, the writing of data to the second track STR1 can be paused. Among the plurality of target sectors RSC of the second track STR1, the remaining target sectors RSC for which the writing of data has been postponed become empty sectors ESC where no data has been written. By avoiding a situation where the positioning error PE exceeds the track margin TM, the occurrence of damaged target sectors CSC in the first track STR0 can be prevented.

[0089] Note that the track STR has servo sectors in addition to the sector SC which is a data sector. In the track STR, generally, the data sectors and the servo sectors are arranged alternately. The write head WHD can derive the positioning error PE together with the servo sectors. Therefore, generally, the positioning error PE is information obtained intermittently.

[0090] In order for PE>TM not to occur, it is necessary to set the write off-track slice WOS so that WOS≦TM. In order to avoid a situation where PE>TM, it is desirable to set the write off-track slice WOS so that WOS<TM. Thereby, before the positioning error PE exceeds the track margin TM, the write process for the second track STR1 can be paused, and a situation where the quality of the data in the first track STR0 deteriorates can be avoided.

[0091] However, it should be noted that the smaller the write-off track slice WOS is set, the more likely the write process will be paused, resulting in a degradation of the write performance of the magnetic disk device 1. In a magnetic disk device 1 that does not have the function of performing error correction on a track-by-track basis, if the write process to the second track STR1 is paused, a write retry process is executed to wait for the disk DK to rotate until PE≦WOS and then resume the write process to the second track STR1. In the write retry process, the empty sectors ESC of the second track STR1 can be changed to recording sectors USC, thereby avoiding a situation in which the utilization efficiency of the second track STR1 remains low.

[0092] 11, it is assumed that all target sectors RSC of the track TR have a common write-off track slice WOS. In the explanation of FIG. 12 described later, it is also assumed that all target sectors RSC of the track TR have a common write-off track slice WOS. However, the setting of the write-off track slice WOS described above is just an example, and the write-off track slice WOS may be different for each target sector RSC.

[0093] 12 is a schematic diagram showing an example of a first track STR0 and a second track STR1 of a magnetic disk device 1 having a function of performing track-by-track error correction on data of a track TR, a diagram for explaining write processing on the first track STR0 and the second track STR1, a diagram for explaining a state in which a judgment value is set to a write-off track slice WOS larger (loose) than the track margin TM, and write processing on the second track STR1 is continued until the track-by-track error correction on the first track STR0 reaches its limit, and a diagram for showing graphs of changes in BER for the first track STR0 and changes in BER with respect to the positioning error PE. For ease of explanation, the first track STR0, etc. are also depicted in FIG. 12 as if the circumferential direction were linear.

[0094] As shown in FIG. 12, the write process for the first track STR0 is ideally performed without a positioning error PE (PE≈0, or PE=0). The magnetic disk device 1 includes an error correction unit 64. When a damaged sector CSC occurs in the track ST, the read processing unit 63, together with the head amplifier IC 130, can detect that the damaged sector CSC has occurred in the track ST, and the error correction unit 64 can execute an error correction process to recover the data in the damaged sector CSC. For example, when a damaged sector CSC occurs in the first track STR0, the error correction unit 64 recovers the data in the damaged sector CSC based on the data in the multiple target sectors RSC in the first track STR0 and the data in the parity sector.

[0095] The parity sector is generated based on the data of a plurality of target sectors RSC in the first track STR0, and can be provided in some of the plurality of target sectors RSC in the first track STR0. For example, one or two target sectors RSC in the first track STR0 can be used as parity sectors. However, the parity sector may be provided in a track TR other than the first track STR0. Alternatively, the parity sector may be provided in a memory other than a disk (for example, non-volatile memory 90).

[0096] As described above, even if a damage-target sector CSC occurs in the first track STR0, the error correction unit 64 can execute error correction processing to recover the data in the damage-target sector CSC, so that the occurrence of the damage-target sector CSC in the first track STR0 can be tolerated. In the magnetic disk device 1 equipped with the error correction unit 64, the write-off track slice WOS can be set so that WOS≧TM, making it difficult for the write process to be terminated and suppressing a deterioration in the write performance of the magnetic disk device 1.

[0097] It should be noted that there is an upper limit in units of tracks TR for the number of damage-target sectors for which the error correction unit 64 can perform error correction in units of tracks TR. For example, if the number of damage-target sectors CSC in the first track STR0 exceeds the upper limit (for example, 5), it becomes difficult for the error correction unit 64 to recover the data in all of the damage-target sectors CSC.

[0098] Fig. 13 is a schematic diagram showing an example of the change in track ECC Gain with respect to the number of squeezes. Fig. 13 is shown in Patent Document 1 (JP 2023-119547 A). As shown in Fig. 13, the horizontal axis labeled "Number of Squeezes" represents the number of damage-target sectors squeezed (written together) within the same track, and the vertical axis labeled "TrackECC Gain" represents the upper limit of the error metric value, which is a measure for predicting the quality of the damage-target sectors. The vertical axis also corresponds to the BER of the damage-target sectors, and the closer to "Large," the worse (larger) the BER is, making it more difficult to read data.

[0099] Here, the error metric value is the excess amount that protrudes from the reference radial position when squeezing is performed from the adjacent track.

[0100] The reference radial position is the adjacent track squeeze position where the BER when the target sector on the target track is read is the threshold BERth (for example, BERth=-1.7), which is the sector ECC correction limit value. Note that the BER is conventionally expressed as a common logarithm (log 10 For example, if the error rate is 1 bit out of 100 bits, BER=log 10 (1 / 100)=-2.0 This becomes:

[0101] If track ECC is not used, it is not possible to write data from adjacent tracks beyond this reference radius position, so the track pitch must be increased accordingly. In other words, the vertical axis in Figure 13 represents the TPI (Track Per Inch) improvement effect of track ECC. If the number of sectors susceptible to damage is small (few squeezes), the average error metric value is large, and data in sectors expected to be more damaged can be saved. On the other hand, if the number of sectors susceptible to damage is large, the average error metric value is small, and it can be seen that only data in sectors expected to be less damaged can be saved.

[0102] 14 is a block diagram showing an example of a positioning control system SY for the head HD and a correction limit prediction unit 65. FIG. 14 is a block diagram based on the configuration disclosed in Patent Document 1.

[0103] 14, the magnetic disk device 1 has a positioning control system SY for the head HD. The positioning control system SY includes a transducer (physical target transducer for writing) TD, a subtractor SU1, a controller CL, and an actuator P.

[0104] The converter TD, the subtractor SU1, and the controller CL are included in, for example, the head amplifier IC 130, the system controller 110, etc. The actuator P is made up of, for example, the arm 30, the VCM 24, etc. The subtractor SU1, the controller CL, and the actuator P make up a feedback system.

[0105] The host 100 specifies the address (C, H, S) of the write target sector to the magnetic disk device 1. Here, for the write target sector, C is the track number (cylinder number), H is the head number, and S is the sector number. The converter TD then converts the address into a distance R corresponding to the track number C and outputs it. The distance R information is input to the subtractor SU1.

[0106] The physical radial position Yr of the head HD can be obtained by reading and demodulating the servo information on the disk DK. The subtractor SU1 outputs the positioning error PE, which is information obtained by subtracting the distance R from the physical radial position Yr, to the controller CL (PE = Yr - R). To achieve stable positioning control in the controller CL, the controller CL applies gain compensation and phase compensation to the positioning error PE to obtain the control amount U. Then, by driving the actuator P using the control amount U as an input, the head HD can be positioned and controlled to the write target position (radial position).

[0107] The error limit prediction unit 65 includes a subtractor SU2, an accumulator Sum, a comparator AM1, a counter COU, and a comparator AM2. The subtractor SU2 outputs an excess amount OVR, which is information obtained by subtracting the track margin TM from the positioning error PE (OVR=PE-TM). When the excess amount OVR is positive, the comparator AM1 outputs an error signal Err, indicating that a damaged sector has occurred. The excess amount OVR is input to the accumulator Sum as a metric value (error metric value) Mer. When the error signal Err is input to the accumulator Sum, the accumulator Sum adds the input metric value Mer and updates the accumulated metric value ME, which is the cumulative total of the metric values ​​Mer.

[0108] Meanwhile, the error signal Err is input to a counter COU, which counts up the number of sectors to be damaged and outputs information ErrC indicating the cumulative total number of sectors to be damaged, and references a table SLT recorded in a memory such as the non-volatile memory 90. The table SLT contains information on the cumulative upper limit threshold CU, which is a variable. From the table SLT, a cumulative upper limit threshold CU corresponding to the information ErrC is selected, and the selected cumulative upper limit threshold CU is input to a comparator AM2 together with the cumulative metric value ME.

[0109] The comparator AM2 can generate prediction information PI, which is information that predicts whether error correction for a data track adjacent to the current write target data track will reach its limit. If the prediction information PI is a positive value (the cumulative metric value ME exceeds the cumulative upper limit threshold CU), it can be predicted that correction by the track ECC will reach its limit, and the judgment unit 66 can make a judgment to end the write process for the current write target data track.

[0110] 14 is an excess amount OVR and does not directly represent the amount of corruption corresponding to the correction capability of the track ECC. This is because the metric value Mer is the degree of corruption of data on adjacent data tracks estimated from the positioning error PE, etc., and the actual degree of corruption cannot be known until the data on the adjacent data tracks is read.

[0111] 15 is a graph illustrating the change in the upper limit excess amount OL and the change in the cumulative upper limit threshold CU for multiple identical sectors with respect to the number N of damage-target sectors in the first track STR0. The upper limit excess amount OL is the upper limit of the excess amount OVR. 15, the cumulative upper threshold CU can be derived from the number N of damage-target sectors and the upper limit excess amount OL. For example, if there are two damage-target sectors within one circumference of a data track, and the excess amount OVR per damage-target sector is up to 6.8 nm (the cumulative upper threshold CU is up to 13.6 nm), data correction for the two damage-target sectors is possible.

[0112] On the other hand, if the number of damaged sectors N within one data track is 10, data correction for the 10 damaged sectors is possible as long as the excess amount OVR per damaged sector is up to 2.7 nm (the cumulative upper threshold CU is up to 27.0 nm). It can be seen that the allowable upper limit excess amount OL decreases as the number of damaged sectors N increases.

[0113] Ideally, the total amount of data corruption that can be tolerated in sectors that are subject to corruption should be constant regardless of the number of sectors that are subject to corruption.

[0114] As shown in Figure 15, however, the cumulative upper threshold CU is small when the number N of damaged sectors is small, and the cumulative upper threshold CU increases as the number N of damaged sectors increases. When using such data, if a series of damaged sectors with small excess OVRs occur in the first half of a write operation on a data track, followed by a damaged sector with a large excess OVR in the middle of the write operation, the error correction limit determination may not be met. This may result in the write operation on the data track being allowed to continue beyond the correction capability of the track ECC.

[0115] The reason why the above situation can occur is because the cumulative upper threshold CU is proportional to the excess amount OVR (positioning error PE). In other words, as can be seen from Figure 12 and other figures, the BER that exceeds the track margin TM is not proportional to the positioning error PE. That is, based on the BER characteristics in Figure 12 and other figures, if we assume that the BER when the excess amount OVR is 2 nm is "1," it can be seen that the BER when the excess amount OVR is 3 nm is not "1.5," but "a value exceeding 1.5."

[0116] From the above, the inventors of the present invention came up with the idea that it is desirable to assign a weight to the larger excess amount OVR in order to correspond to the BER characteristics, as this makes it easier to determine the true correction limit, and have come up with a concrete implementation of this idea. The weighting and other aspects will be described later.

[0117] 16 is a graph illustrating the cumulative value of the number N of damage-target sectors in the first track STR0 and the excess amount OVR of each damage-target sector. In FIG. 16, the horizontal axis represents the order in which the damage-target sectors occur. For example, the excess amount OVR at N=5 is the value when the damage-target sector occurs for the fifth time.

[0118] For example, consider a case where all of the damaged sectors that occurred from the first to fourth times were caused by an excess OVR of 1 nm, and all of the damaged sectors that occurred from the fifth time onwards were caused by an excess OVR of 6 nm.

[0119] Fig. 17 is a graph illustrating the change in the cumulative metric value ME with respect to the number N of damage-target sectors in the first track STR0, and also shows a graph illustrating the change in the cumulative upper limit threshold CU shown in Fig. 15. In Fig. 17, the cumulative metric value ME is based on the data in Fig. 16.

[0120] As shown in Figure 17, the cumulative metric value ME exceeds the cumulative upper limit threshold CU and the prediction information PI becomes positive when the eighth prediction of a damaged sector occurs. However, the excess amount OVR from the fifth to the seventh prediction of a damaged sector is 6 nm for three consecutive times. On the other hand, based on Figure 15, when there are three damaged sectors, the excess amount OL is 5.3 nm, and the above 6 nm cannot be tolerated.

[0121] 15 and 16, it can be seen that, unlike in Fig. 17, it would be preferable for the judgment unit 66 to judge that the write process to the data track should be terminated when the seventh prediction of the occurrence of a sector to be damaged is made. However, in the example of Fig. 17, the continuation of the write process that would cause the seventh sector to be damaged is permitted, so the judgment unit 66 permits the continuation of the write process to the data track to an extent that exceeds the correction capability of the track ECC.

[0122] The reason why the timing for ending the write process is inappropriate is because the idea of ​​weighting was not considered. As described above, the inventors of the present application have come up with the idea that weighting should be applied to the excess amount OVR in order to solve the above-mentioned problem. For example, the inventors of the present application have come up with the idea that the larger the excess amount OVR (the greater the degree of damage), the more weight should be applied to the excess amount OVR. This enables the magnetic disk device 1 to accurately determine the correction limit using the track ECC.

[0123] Next, the write processing method according to this embodiment will be described together with the configuration of the magnetic disk device 1. Fig. 18 is a block diagram showing an example of a head positioning control system and a correction limit prediction unit according to this embodiment.

[0124] 18, 1, and 12, the magnetic disk device 1 has a positioning control system SY for the head HD. The positioning control system SY shown in FIG. 18 is the same as the positioning control system SY shown in FIG.

[0125] The write processing unit 62 can select a shingled recording format in which data of the second track STR1 is written overlapping data of the first track STR0 in an overwrite direction d5 parallel to the radial direction d1 of the disk DK.

[0126] Here, in a direction parallel to the radial direction d1 of the disk DK, the first track STR0 is located in a first direction Da as viewed from the second track STR1. Here, the first direction Da coincides with the radial direction d1, but it may be the opposite direction to the radial direction d1. In the first direction Da, a position that is a track margin TM away from a position where the positioning error PE is 0 is defined as a reference radial position PTM. When the position of the write head WHD protrudes from the reference radial position PTM in the first direction Da during the write period, the correction limit prediction unit 65 can determine that the target sector RSC adjacent to the write head WHD in the first direction Da among the multiple target sectors RSC of the first track STR0 is a damaged target sector CSC.

[0127] The error correction unit 64 can perform error correction on data in one or more damaged target sectors CSC that are determined to have damaged data among the plurality of target sectors RSC in the first track STR0. Unlike FIG. 14, the error limit prediction unit 65 does not include a counter COU, but further includes a variable gain amplifier AM3.

[0128] Here, attention is focused on a write period in which a write process is executed on a plurality of target sectors RSC of the first track STR0 and then a write process is executed on a plurality of target sectors RSC of the second track STR1.

[0129] First, the correction limit prediction unit 65 calculates an excess amount OVR by which the position of the write head (first write head) WHD protrudes in the first direction Da from the reference radial position (first reference radial position) PTM each time data is written to each target sector RSC of the second track STR1. In this embodiment, the subtractor SU2 outputs the excess amount OVR, which is information obtained by subtracting the track margin TM from the positioning error PE (OVR=PE-TM).

[0130] Next, the correction limit prediction unit 65 calculates a metric value Mer by multiplying the excess amount OVR by a first weighting coefficient W1, which is a variable whose value changes depending on the excess amount OVR, each time the position of the write head WHD exceeds the reference radial position PTM. In this embodiment, the variable gain amplifier AM3 is configured so that its gain changes depending on the input excess amount OVR, and can output a signal of the metric value Mer (Mer=0×W1).

[0131] Next, the correction limit prediction unit 65 updates the cumulative metric value ME, which is the cumulative total of the metric values ​​Mer during the write period. In this embodiment, when the excess amount OVR is a positive value, the comparator AM1 outputs an error signal Err, indicating that a damaged sector has occurred. The metric value (error metric value) Mer is output from the variable gain amplifier AM3 and input to the accumulator Sum. Then, when the error signal Err is input to the accumulator Sum, the accumulator Sum adds the input metric value Mer and updates the cumulative metric value ME.

[0132] Thereafter, the correction limit prediction unit 65 generates prediction information (first prediction information) PI, which is information for predicting whether error correction for the first track STR0 will reach its limit based on the accumulated metric value ME before the write process for all target sectors RSC of the second track STR1 is completed. In this embodiment, a signal (value) indicating the accumulated metric value ME is input from the integrator Sum to one input terminal of the comparator AM2. The value input to the other input terminal of the comparator AM2 is a reference value and is fixed. Here, the reference value is a fixed value that indicates a specific reference value RV, which is a constant. If the prediction information PI output by the comparator AM2 is a positive value (the accumulated metric value ME exceeds the specific reference value RV), it can be predicted that correction by the track ECC will reach its limit.

[0133] The determination section 66 can determine whether to allow the write processing section 62 to continue the write process on the second track STR1 based on the prediction information PI. Therefore, it is possible to obtain a magnetic disk device 1 that can predict whether error correction for the first track STR0 of the disk DK will reach its limit.

[0134] 18 is a value obtained by multiplying the excess amount OVR by the first weighting factor W1, and roughly represents the amount of corruption corresponding to the correction capability of the track ECC. Therefore, the magnetic disk device 1 can more accurately determine the correction limit of the track ECC.

[0135] Providing the magnetic disk device 1 with the option to continue the write process makes it possible to suppress a decrease in the write performance of the magnetic disk device 1. Furthermore, providing the magnetic disk device 1 with the option to end the write process makes it possible to prevent excessive corruption of the data in the first track STR0, and to avoid a situation in which the amount of corrupted data in the first track STR0 exceeds a limit.

[0136] The correction limit prediction unit 65 can predict the correction limit of the track ECC based on the specific reference value RV. When the correction limit prediction unit 65 predicts that the accumulated metric value ME will not reach the specific reference value RV, the prediction information PI indicates normal information that predicts that error correction will not reach its limit. On the other hand, when the correction limit prediction unit 65 predicts that the accumulated metric value ME will reach the specific reference value RV, the prediction information PI indicates abnormal information that predicts that error correction will reach its limit.

[0137] The switching unit 67 can set the error correction mode to an effective mode that enables the error correction unit 64 to perform error correction on a track-by-track basis. If the prediction information PI indicates normal information during the write period, the switching unit 67 sets the error correction mode to the effective mode, and the determination unit 66 can cause the write processing unit 62 to continue the write process for the second track STR1. For example, if the magnetic disk device 1 is not in a vibrating state, the determination unit 66 can determine to cause the write processing unit 62 to continue the write process.

[0138] The switching unit 67 can switch the error correction mode for each track to the valid mode or an invalid mode that invalidates the error correction mode. If the prediction information PI changes to abnormal information during the write period, the switching unit 67 switches the error correction mode to the invalid mode, and the determination unit 66 can cause the write processing unit 62 to end the write process for the second track STR1.

[0139] The specific reference value RV is a positive value. In this case, the excess amount OVR increases as the position of the write head WHD protrudes from the reference radial position PTM in the first direction Da. It is also desirable that the first weighting coefficient W1 monotonically increases, and that the first weighting coefficient W1 also increases as the excess amount OVR increases. As can be seen from FIG. 12 above, this is because when the positioning error PE exceeds the track margin TM, the BER increases quadratically. Because the BER does not increase linearly, the weighting described above is necessary; otherwise, accurate physical evaluation would be impossible.

[0140] The first weighting coefficient W1 is a linear function of the excess amount OVR. However, the first weighting coefficient W1 is not limited to being a linear function of the excess amount OVR, and can be variously modified as long as it monotonically increases. For example, the first weighting coefficient W1 may be a quadratic function of the excess amount OVR.

[0141] First information indicating the correspondence between the excess amount OVR and the first weighting factor W1 may be recorded in, for example, the nonvolatile memory 90 as the storage unit of the magnetic disk device 1. When deriving the first weighting factor W1, the correction limit prediction unit 65 can derive the first weighting factor W1 corresponding to the calculated excess amount OVR based on the first information recorded in the nonvolatile memory 90. As can be seen from the above, the value of the first weighting coefficient W1 when the excess amount OVR is 6 nm is different from the value of the first weighting coefficient W1 when the excess amount OVR is 4 nm. More specifically, the value of the first weighting coefficient W1 when the excess amount OVR is 6 nm is greater than the value of the first weighting coefficient W1 when the excess amount OVR is 4 nm.

[0142] Next, the relationship between the number N of sectors to be damaged, the first weighting factor W1, the upper limit excess amount OL, the cumulative upper limit threshold CU, and the like will be described.

[0143] If a case where the determination unit 66 determines that Nr damaged sectors CSC have occurred in the first track STR0 during the write process on the second track STR1 is taken as a reference case, then the following applies.

[0144] ·Amount exceeding the upper limit: OL(Nr) First weighting factor: W1(Nr) W1(Nr)=1 Accumulation upper threshold: CU(Nr) Accumulated metric value: ME(Nr) W1(Nr)=CU(Nr) / ME(Nr)=1

[0145] Then, W1(Nr)×OL(Nr)×Nr=W1(Nr)×CU(Nr)=specific reference value RV.

[0146] Next, in the write process for the second track STR1, if the case where the determination unit 66 determines that N1 damaged sectors CSC have occurred in the first track STR0 is taken as the target case, then the following will be applied.

[0147] ·Amount exceeding the upper limit: OL(N1) First weighting factor: W1(N1) Accumulation upper threshold: CU(N1) Accumulated metric value: ME(N1) W1(N1)=CU(N1) / ME(N1)

[0148] Then, W1(N1)×OL(N1)×N1=W1(N1)×CU(N1)=the specific reference value RV.

[0149] From the above, W1(N1)=CU(Nr) / CU(N1) This becomes: By determining the reference first weighting factor W1(Nr) which is 1, it is possible to determine not only the reference number Nr of damage target sectors CSC but also the reference upper limit excess amount OL(Nr).

[0150] Also, as mentioned above, W1(Nr) × OL(Nr) × Nr = W1(Nr) × CU(Nr), and From W1(Nr) = 1, CU(Nr) = OL(Nr) × Nr it follows that.

[0151] Next, assume a case where the excess amount OL(N1) exceeding the upper limit is greater than the reference excess amount OL(Nr). In the write process for the second track STR1, when the excess amount OVR becomes the excess amount OL(N1) exceeding the upper limit, and the determination unit 66 determines that one damaged target sector CSC has occurred in the first track STR0, and moreover, when OL(N1) > OL(Nr), the correction limit prediction unit 65 performs the following processing.

[0152] That is, the correction limit prediction unit 65 calculates the excess amount OL(N1) which is the excess amount OVR, calculates the metric value Mer(N1) by multiplying the first weight coefficient W1(N1) by the excess amount OL(N1), and updates the cumulative metric value ME(N1). In that case, W1(N1) > W1(Nr) holds, and CU(N1) < CU(Nr) holds.

[0153] Next, assume a case where the excess amount OL(N1) exceeding the upper limit is smaller than the reference excess amount OL(Nr). In the write process for the second track STR1, when the excess amount OVR becomes the excess amount OL(N1) exceeding the upper limit, and the determination unit 66 determines that one damaged target sector CSC has occurred in the first track STR0, and moreover, when OL(N1) < OL(Nr), the correction limit prediction unit 65 performs the following processing.

[0154] That is, the correction limit prediction unit 65 calculates the excess amount OL(N1) which is the excess amount OVR, calculates the metric value Mer(N1) by multiplying the first weight coefficient W1(N1) by the excess amount OL(N1), and updates the cumulative metric value ME(N1). In that case, 0 < W1(N1) < W1(Nr) holds, and CU(N1) > CU(Nr) holds.

[0155] Next, the relationship between the excess amount OVR and the first weighting factor W1 will be described. Figure 19 is a graph showing the change in the first weighting factor W1 relative to the excess amount OVR. In Figure 19, the number of damaged sectors CSC in the correction limit of the first track STR0 is set to 10 (Nr=10). Here, based on FIG. 15, when the number N of damage target sectors CSC is 10, the upper limit excess amount OL is 2.66 nm.

[0156] On the other hand, as shown in Fig. 19, when the excess amount OVR is 2.66 nm, the first weighting coefficient W1(Nr) is 1.0. If the first weighting coefficient W1 is y and the excess amount OVR is x, then the following applies to the first weighting coefficient W1: y=0.24×x+0.36 Therefore, the first weighting coefficient W1 can be approximated by a linear function. Therefore, as described above, the first weighting coefficient W1 can be recorded as a function in a storage unit such as the nonvolatile memory 90.

[0157] 19, when the excess amount OVR is 4 nm, N1=5, and the first weighting coefficient W1(N1) is effectively 1.3. This value of 1.3 can be calculated based on FIG. 15 and the following relational expression described above. W1(N1)=CU(Nr) / CU(N1) Nr=10 N1=5

[0158] Based on Figure 15, CU(10) = 26.6 nm and CU(5) = 20 nm, so W1(5)=CU(10) / CU(5)=26.6nm / 20nm≒1.3 And A first weighting factor W1(5) of substantially 1.3 can be calculated.

[0159] Next, we will explain the average value and cumulative metric value ME of the metric value Mer calculated using the correction limit prediction unit 65 of Figure 14, and the average value and cumulative metric value ME of the metric value Mer calculated using the correction limit prediction unit 65 of Figure 18 (this embodiment), while comparing them.

[0160] Fig. 20 is a graph showing two examples of changes in the average value of the metric value Mer with respect to the number of sectors CSC to be damaged. Fig. 21 is a graph showing two examples of changes in the upper limit value of the cumulative metric value ME with respect to the number of sectors CSC to be damaged.

[0161] As shown in Figure 20, in contrast to the correction limit prediction method of Figure 14 which does not use a weighting factor, in the correction limit prediction method of this embodiment of Figure 18 which uses a weighting factor, the metric value Mer is weighted more as the excess amount OVR is larger. As shown in Fig. 21, and in the correction limit prediction method of this embodiment shown in Fig. 18, the upper limit of the cumulative metric value ME is 26.63 nm regardless of the number of damaged sectors CSC. In other words, it can be seen that the specific reference value RV should be set (fixed) to 26.63 nm.

[0162] Next, the metric value Mer calculated using the correction limit prediction unit 65 in Fig. 14 will be explained while comparing it with the metric value Mer calculated using the correction limit prediction unit 65 in Fig. 18 (this embodiment). Fig. 22 is a diagram illustrating two types of graphs showing the cumulative value of the number of damage target sectors CSC in the first track STR0 and the individual metric values ​​Mer.

[0163] In Fig. 22, the horizontal axis is arranged in the order in which the damage target sectors occur, as in Fig. 16. Let us consider a case in which the damage target sectors CSC that occurred from the first to fourth times were all caused by an excess OVR of 1 nm, and the damage target sectors CSC that occurred from the fifth time onwards were all caused by an excess OVR of 6 nm.

[0164] As shown in Fig. 22, in the correction limit prediction method of this embodiment of Fig. 18, when the excess amount OVR is 1 nm, the first weighting factor W1 is a positive value less than 1.0, so the metric value Mer can be set to a value less than 1 nm. Similarly, when the excess amount OVR is 6 nm, the first weighting factor W1 is a value greater than 1.0, so the metric value Mer can be set to a value greater than 6 nm. Based on Fig. 19, when the excess amount OVR is 6 nm, the first weighting factor W1 is preferably 1.8, so when the metric value Mer is calculated, Mer=W1×OVR=1.8×6nm=10.8nm This becomes:

[0165] Next, the cumulative metric value ME calculated using the correction limit prediction unit 65 of Fig. 18 (this embodiment) will be described. Fig. 23 is a graph illustrating the change in the cumulative metric value ME with respect to the number of damage-target sectors CSC of the first track STR0, and also shows a graph in which the upper limit value (specific reference value RV) of the cumulative metric value ME shown in Fig. 21 is constant. Note that in Fig. 23, the cumulative metric value ME is based on the data of this embodiment in Fig. 22.

[0166] As shown in Figure 23 and Figures 19 to 22, all of the damaged sectors that occurred from the first to fourth times were caused by an excess OVR of 1 nm, and all of the damaged sectors that occurred from the fifth time onwards were caused by an excess OVR of 6 nm.

[0167] Based on FIG. 19, when the excess amount OVR is 1 nm, the first weighting coefficient W1 is preferably 0.6, so when the metric value Mer is calculated, Mer=W1×OVR=0.6×1nm=0.6nm This becomes:

[0168] When it is predicted that the first four damaged sectors CSC will occur, the cumulative metric value ME is: ME=0.6nm+0.6nm+0.6nm+0.6nm=2.4nm will be updated to.

[0169] Thereafter, when the fifth and sixth occurrences of the damaged sector CSC are predicted, the cumulative metric value ME is: ME=2.4nm+10.8nm+10.8nm=24.0nm will be updated to.

[0170] If the cumulative metric value ME is 24.0 nm, the cumulative metric value ME is equal to or less than the specific reference value RV (26.63 nm), and therefore the determination unit 66 can allow the write process that will result in the sixth occurrence of a damage target sector CSC.

[0171] Furthermore, when the seventh damaged sector CSC is predicted to occur, the cumulative metric value ME is: ME=24.0nm+10.8nm=34.8nm will be updated to.

[0172] When the cumulative metric value ME reaches 34.8 nm, the cumulative metric value ME exceeds the specific reference value RV (26.63 nm), so the judgment unit 66 can prohibit the write process that would result in the occurrence of the seventh damaged sector CSC and terminate the write process.

[0173] Here, referring to Figure 15, when the number N of damage-target sectors CSC is 2, the upper limit excess amount OL(2) is 6.7 nm, so the judgment unit 66 can allow damage-target sectors CSC to occur twice due to the 6 nm excess amount OVR, and can allow a write process that will result in the occurrence of a sixth damage-target sector CSC. On the other hand, when the number N of damage-target sectors CSC is 3, the upper limit excess amount OL(3) is 5.4 nm, so the judgment unit 66 can prohibit the occurrence of damage-target sectors CSC caused by the 6 nm excess amount OVR three times, and can prohibit a write process that would result in the occurrence of a damage-target sector CSC for the seventh time. From the above, it can be seen that the correction limit prediction method of the magnetic disk device 1 of this embodiment can more accurately determine the correction limit using the track ECC.

[0174] According to the magnetic disk device 1, write processing method, and correction limit prediction method of the first embodiment configured as described above, the magnetic disk device 1 comprises a disk DK, a write head WHD, a write processing unit 62, an error correction unit 64, a correction limit prediction unit 65, and a judgment unit 66.

[0175] During the write period, the correction limit prediction unit 65 Each time data is written to each target sector RSC of the second track STR1, the excess amount OVR is calculated. Each time the position of the write head WHD exceeds the reference radial position PTM, the metric value Mer is calculated by multiplying the excess amount OVR by the first weighting coefficient W1. The cumulative metric value ME is updated, and prediction information PI is generated until the write process to all target sectors RSC of the second track STR1 is completed.

[0176] The determination section 66 can determine whether to allow the write processing section 62 to continue the write process on the second track STR1 based on the prediction information PI. This makes it possible to obtain a magnetic disk device 1 that can predict whether error correction for the data tracks of the disk DK will reach its limit. Before the amount of data corruption in the first track STR0 exceeds the limit (specific reference value RV), the determination unit 66 can determine whether to continue or terminate the write process for the second track STR1.

[0177] (Second embodiment) Next, a second embodiment will be described. The magnetic disk device 1 has the same configuration as the magnetic disk device 1 of the first embodiment, except for the configuration described in this second embodiment. The write processing method and the correction limit prediction method are the same as the write processing method and the correction limit prediction method of the first embodiment, except for the procedures described in this second embodiment.

[0178] 24 is a schematic diagram showing an example of the third track STRα0 and the fourth track STRα1 of the magnetic disk device 1 according to the second embodiment, and is a diagram for explaining the write processing for the third track STRα0 and the fourth track STRα1, and is a diagram for explaining a state in which the judgment value is set to a write-off track slice WOS that is larger (loose) than the track margin TM, and the write processing for the fourth track STRα1 is continued until the track-by-track error correction for the third track STRα0 reaches its limit, and is a diagram showing, in graphs, the change in BER for the third track STRα0 and the change in BER with respect to the positioning error PE. For ease of explanation, in FIG. 24, the third track STRα0, etc. are also drawn as if the circumferential direction were linear.

[0179] As shown in FIG. 24, the write process for the third track STRα0 is ideally executed without a positioning error PE (PE≈0, or PE=0). In this embodiment, the weighting factor W is adjustable for each zone Z of the recording layer L of the disc DK.

[0180] The recording layer L of the disk DK has a zone (first zone) Ze including a first track STR0 and a second track STR1, and a zone (second zone) Zeα including a third track STRα0 and a fourth track STRα1. The third track STRα0 and the fourth track STRα1 are adjacent to each other and each include a plurality of target sectors RSC. The third track STRα0 is located in a second direction Db parallel to the radial direction d1 when viewed from the fourth track STRα1. Here, the second direction Db coincides with the radial direction d1, but it may also be the opposite direction to the radial direction d1.

[0181] Here, attention is focused on a write period in which a write process is executed on a plurality of target sectors RSC of the third track STRα0 and then a write process is executed on a plurality of target sectors RSC of the fourth track STRα1.

[0182] First, the correction limit prediction unit 65 calculates the excess amount OVR by which the position of the write head (first write head) WHD protrudes from the second reference radial position PTM in the second direction Db each time data is written to each target sector RSC of the fourth track STRα1. Next, the correction limit prediction unit 65 calculates the metric value Mer by multiplying the excess amount OVR by a second weighting coefficient W2, which is a variable whose value changes depending on the excess amount OVR, each time the position of the write head WHD exceeds the second reference radial position PTM.

[0183] Next, the error limit prediction unit 65 updates the cumulative metric value ME, which is the cumulative total of the metric values ​​Mer during the write period. Thereafter, the correction limit prediction unit 65 generates second prediction information PI, which is information that predicts whether error correction for the third track STRα0 will reach its limit based on the cumulative metric value ME before completing the write process for all target sectors RSC of the fourth track STRα1. The determination section 66 can determine whether to allow the write processing section 62 to continue the write process on the fourth track STRα1 based on the second prediction information PI.

[0184] The magnetic disk device 1, write processing method, and error limit prediction method according to the second embodiment configured as described above can also achieve the same effects as those of the first embodiment.

[0185] The weighting factor W can be adjusted for each zone Z of the recording layer L of the disc DK. For example, the first weighting coefficient W1 and the second weighting coefficient W2 may be the same. In this case, the first weighting coefficient W1 and the second weighting coefficient W2 may be the data of the graph shown in FIG. Alternatively, the second weighting coefficient W2 may be a coefficient different from the first weighting coefficient W1. This allows the error correction limit of the track ECC to be determined more accurately.

[0186] In this case, as a memory unit of the magnetic disk device 1, for example, a non-volatile memory 90 may record first information indicating the correspondence between the excess amount OVR and the first weighting coefficient W1, and second information indicating the correspondence between the excess amount OVR and the second weighting coefficient W2. As a result, during the write period in which write processing is performed on the second track STR1, the correction limit prediction unit 65 can derive the first weighting coefficient W1 corresponding to the calculated excess amount OVR based on the above-mentioned first information recorded in the non-volatile memory 90. In addition, during the write period when write processing is performed on the fourth track STRα1, the correction limit prediction unit 65 can derive the second weighting coefficient W2 corresponding to the calculated excess amount OVR based on the above-mentioned second information recorded in the non-volatile memory 90.

[0187] (Modification 1 of the second embodiment) Next, a first modification of the second embodiment will be described. The magnetic disk device 1 has the same configuration as the magnetic disk device 1 of the second embodiment, except for the configuration described in this first modification. The write processing method and the correction limit prediction method are the same as the write processing method and the correction limit prediction method of the second embodiment, except for the procedures described in this first modification. In this first modification, the weighting factor W may be adjusted for each head HD instead of for each zone Z.

[0188] The second recording layer L of the second disk DK may have a third track STRα0 and a fourth track STRα1. The second write head WHD writes data to the second recording layer L. The first disc DK having the first recording layer L (first track STR0 and second track STR1) and the second disc DK having the second recording layer L may be the same disc. In that case, the second recording layer L may be the recording layer on the opposite side of the first recording layer L. Alternatively, the first disc DK and the second disc DK may be different discs. In that case, as shown in FIG. 2, for example, the first recording layer L is the first recording layer La1 of the disc DK1, and the second recording layer L is the second recording layer Lb2 of the disc DK2.

[0189] The same effects as those of the second embodiment can be obtained in this modified example 1. Furthermore, the error correction limit based on the track ECC can be determined more accurately for each head HD.

[0190] (Modification 2 of the second embodiment) Next, a description will be given of a modified example 2 of the second embodiment. The magnetic disk device 1 has the same configuration as the magnetic disk device 1 of the second embodiment, except for the configuration described in this modified example 2. The write processing method and the correction limit prediction method are the same as the write processing method and the correction limit prediction method of the second embodiment, except for the procedure described in this modified example 2.

[0191] In the present modified example 2, the weighting factor W may be adjusted for each zone Z, and may also be adjusted for each head HD. In this modification 2, it is possible to obtain the same effects as those of the second embodiment and modification 2. Furthermore, it is possible to more accurately determine the error limit by track ECC for each head HD and for each zone Z.

[0192] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims.

[0193] For example, the above-described technique is not limited to being applied to hybrid recording type magnetic disk devices, but may also be applied to shingled recording type magnetic disk devices and normal recording type magnetic disk devices. [Explanation of symbols]

[0194] 1...magnetic disk device, 60...MPU, 61...read / write processing unit, 62...write processing unit, 63...read processing unit, 64...error correction unit, 65...correction limit prediction unit, 66...judgment unit, 67...switching unit, 70...volatile memory, 80...buffer memory, 90...non-volatile memory, 100...host, 110...system controller, 120...driver IC, 130...head amplifier IC, 140...R / W channel, 150...HDC, 24...VCM, 30...arm, DK...disk, L...recording layer, TR, STR, CTR...track, SC...sector, RSC...target sector, CSC... Damaged sector, HD...head, WHD...write head, RHD...read head, AM1, AM2...comparator, AM3...variable gain amplifier, SU...subtractor, Sum...accumulator, Z...zone, PE...positioning error, TM...track margin, PTM...reference radial position, OVR...excess amount, OL...excess amount above upper limit, Mer...metric value, ME...accumulated metric value, CU...accumulated upper limit threshold, PI...prediction information, RV...specific reference value, N, Nr, N1...number, W...weighting coefficient, d1...radial direction, d2...traveling direction, d3...rotational direction, d5...overwrite direction, Da...first direction, Db...second direction.

Claims

1. a first disk having a first data track and a second data track adjacent to each other on a first recording layer, the first data track and the second data track each including a plurality of target sectors to which data is written, the first data track being positioned in a first direction parallel to a radial direction of the first disk as viewed from the second data track; a first write head that writes data to the first recording layer of the first disk; a write processing unit capable of executing a write process for writing data to the first recording layer; an error correction unit that performs error correction on data in one or more damaged target sectors determined to have damaged data among the plurality of target sectors of the first data track; a correction limit prediction unit; a determination unit, During a write period in which the write process is performed on the plurality of target sectors of the first data track and then the write process is performed on the plurality of target sectors of the second data track, The correction limit prediction unit calculating an excess amount by which the position of the first write head protrudes from a first reference radial position in the first direction every time data is written to the target sector of each of the second data tracks; calculating a metric value by multiplying the excess amount by a first weighting coefficient, which is a variable whose value changes depending on the excess amount, every time the position of the first write head exceeds the first reference radial position; updating a cumulative metric value that is a cumulative total of the metric values ​​during the write period; generating first prediction information that predicts whether the error correction for the first data track will reach a limit based on the cumulative metric value until the write process for all target sectors of the second data track is completed; the determination unit determines whether to cause the write processing unit to continue the write process on the second data track based on the first prediction information; Magnetic disk device.

2. when the correction limit prediction unit predicts that the cumulative metric value will not reach a specific reference value that is a constant, the first prediction information indicates normal information that predicts that the error correction will not reach a limit, when the correction limit prediction unit predicts that the cumulative metric value will reach the specific reference value, the first prediction information indicates abnormality information that predicts that the error correction will reach its limit; 2. The magnetic disk drive according to claim 1.

3. a switching unit that can be set to an effective mode that enables the error correction unit to perform error correction on a track-by-track basis; If the first prediction information indicates the normal information during the write period, the switching unit sets the error correction mode to the valid mode, the determination unit causes the write processing unit to continue the write process on the second data track; 3. The magnetic disk drive according to claim 2.

4. the switching unit is capable of switching the error correction mode to the valid mode or an invalid mode that invalidates the error correction mode, If the first prediction information is changed to the abnormality information during the write period, the switching unit switches the error correction mode to the invalid mode, the determination unit causes the write processing unit to end the write process on the second data track; 4. The magnetic disk drive according to claim 3.

5. The specific reference value is a positive value, the excess amount increases as the position of the first write head protrudes from the first reference radial position in the first direction, The first weighting coefficient monotonically increases, and the larger the excess amount, the larger the first weighting coefficient.

3. The magnetic disk drive according to claim 2.

6. the first weighting factor is a linear function of the excess amount; 6. The magnetic disk drive according to claim 5.

7. the first weighting factor is a quadratic function of the excess amount; 6. The magnetic disk drive according to claim 5.

8. a storage unit in which first information indicating a correspondence relationship between the excess amount and the first weighting coefficient is recorded; When deriving the first weighting coefficient, the correction limit prediction unit derives the first weighting coefficient corresponding to the calculated excess amount based on the first information recorded in the storage unit.

8. The magnetic disk drive according to claim 5.

9. In the write process for the second data track, when the case in which the determination unit determines that Nr damaged sectors have occurred in the first data track is taken as a reference case, The upper limit of the excess amount is OL(Nr), The first weighting factor is W1(Nr), W1(Nr)=1, The cumulative upper threshold is CU(Nr), The cumulative metric value is ME(Nr), If W1(Nr)=CU(Nr) / ME(Nr)=1, then W1(Nr)×OL(Nr)×Nr=W1(Nr)×CU(Nr)=specific reference value, In the write process for the second data track, when the case in which the determination unit determines that N1 damaged sectors have occurred in the first data track is taken as a target case, The upper limit of the excess amount is OL(N1), The first weighting factor is W1(N1), The cumulative upper threshold is CU(N1), The cumulative metric value is ME(N1), If W1(N1)=CU(N1) / ME(N1), then W1(N1)×OL(N1)×N1=W1(N1)×CU(N1)=the specific reference value, W1(N1)=CU(Nr) / CU(N1), 2. The magnetic disk drive according to claim 1.

10. CU(Nr)=OL(Nr)×Nr=the specific reference value; 10. The magnetic disk drive according to claim 9.

11. In the write process for the second data track, if the excess amount becomes the upper limit excess amount OL(N1), the determination unit determines that one damaged sector has occurred in the first data track, and OL(N1)>OL(Nr), The correction limit prediction unit Calculating the upper limit excess amount OL(N1), which is the excess amount; calculate the metric value ME(N1) by multiplying the upper limit excess amount OL(N1) by the first weighting coefficient W1(N1); updating the cumulative metric value ME(N1); W1(N1)>W1(Nr), CU(N1)<CU(Nr); 10. The magnetic disk drive according to claim 9.

12. In the write process for the second data track, if the excess amount becomes the upper limit excess amount OL(N1), the determination unit determines that one damaged sector has occurred in the first data track, and OL(N1)<OL(Nr), The correction limit prediction unit Calculating the upper limit excess amount OL(N1), which is the excess amount; calculate the metric value ME(N1) by multiplying the upper limit excess amount OL(N1) by the first weighting coefficient W1(N1); updating the cumulative metric value ME(N1); 0<W1(N1)<W1(Nr), CU(N1)>CU(Nr); 10. The magnetic disk drive according to claim 9.

13. the first recording layer of the first disk has a first zone including the first data track and the second data track, and a second zone having a third data track and a fourth data track adjacent to each other and each including the plurality of target sectors; the third data track is located in a second direction parallel to the radial direction when viewed from the fourth data track, During a write period in which the write process is performed on the plurality of target sectors of the third data track and then the write process is performed on the plurality of target sectors of the fourth data track, The correction limit prediction unit calculating an excess amount of the position of the first write head protruding from a second reference radial position in the second direction every time data is written to the target sector of the fourth data track; calculating a metric value by multiplying the excess amount by a second weighting coefficient, which is a variable whose value changes depending on the excess amount, every time the position of the first write head exceeds the second reference radial position; updating a cumulative metric value that is a cumulative total of the metric values ​​during the write period; generating second prediction information that predicts whether the error correction for the third data track will reach a limit based on the cumulative metric value before the write process for all target sectors of the fourth data track is completed; the determination unit determines whether to cause the write processing unit to continue the write process on the fourth data track based on the second prediction information.

2. The magnetic disk drive according to claim 1.

14. a second recording layer having a third data track and a fourth data track adjacent to each other, the third data track and the fourth data track each including a plurality of target sectors to which data is written, the third data track being positioned in a second direction parallel to the radial direction as viewed from the fourth data track; a second write head that writes data to the second recording layer, the second recording layer is formed on the opposite side of the first recording layer of the first disc, or is formed on a second disc different from the first disc; the write processing unit is capable of executing a write process for writing data to the second recording layer, the error correction unit performs error correction on data in one or more damaged target sectors determined to have damaged data among the plurality of target sectors of the third data track; During a write period in which the write process is performed on the plurality of target sectors of the third data track and then the write process is performed on the plurality of target sectors of the fourth data track, The correction limit prediction unit calculating an excess amount by which the position of the second write head protrudes from a second reference radial position in the second direction every time data is written to the target sector of each of the fourth data tracks; calculating a metric value by multiplying the excess amount by a second weighting coefficient, which is a variable whose value changes depending on the excess amount, every time the position of the second write head exceeds the second reference radial position; updating a cumulative metric value that is a cumulative total of the metric values ​​during the write period; generating second prediction information that predicts whether the error correction for the third data track will reach a limit based on the cumulative metric value before the write process for all target sectors of the fourth data track is completed; the determination unit determines whether to cause the write processing unit to continue the write process on the fourth data track based on the second prediction information.

2. The magnetic disk drive according to claim 1.

15. The first weighting coefficient and the second weighting coefficient are equal to each other.

15. The magnetic disk drive according to claim 13 or 14.

16. the second weighting coefficient is a coefficient different from the first weighting coefficient; 15. The magnetic disk drive according to claim 13 or 14.

17. a storage unit in which first information indicating a correspondence relationship between the excess amount and the first weighting coefficient and second information indicating a correspondence relationship between the excess amount and the second weighting coefficient are recorded; During a write period in which the write process is performed on the second data track, the correction limit prediction unit derives the first weighting coefficient corresponding to the calculated excess amount based on the first information recorded in the storage unit; During a write period in which the write process is performed on the fourth data track, the correction limit prediction unit derives the second weighting coefficient corresponding to the calculated excess amount based on the second information recorded in the storage unit.

17. The magnetic disk drive according to claim 16.

18. the write processing unit is capable of selecting a shingled recording format in which data of the second data track is written overlapping data of the first data track in an overwrite direction parallel to the radial direction of the first disk.

2. The magnetic disk drive according to claim 1.

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