STORAGE SYSTEM, METHOD AND PROGRAM FOR CONTROLLING CACHE IN STORAGE SYSTEM

Abstract

To provide a storage system that can back up cache data while eliminating vulnerability of the storage system even when a part or a plurality of nonvolatile memories constituting a backup memory fail. The storage system includes a cache controller and a backup memory controller. When a backup memory, which is made up of multiple nonvolatile memories, has a failed nonvolatile memory, the backup memory controller calculates the amount of data that can be evacuated from the cache memory in the nonvolatile memories other than the failed nonvolatile memory. The cache controller controls the amount of data written to the cache memory, with the calculated amount of data set as an upper limit.

Description

[Technical field]

[0001] The present disclosure relates to a storage system, and a cache control method and program for a storage system. [Background technology]

[0002] With the development of information technology, the amount of information handled is increasing dramatically. Accordingly, the need for large-capacity, high-density storage systems is growing. The handling of data in these storage systems is generally managed by a file system. When writing data, it is necessary to write to a disk drive, but when performing temporary processing to ensure performance, cache memory installed in the storage including the disk drive is used. When using cache memory, if the power supply is interrupted, the data in the cache memory may be lost. For this reason, it is common to prevent data loss by installing a battery in the storage system and saving the data to non-volatile memory.

[0003] Non-volatile memory with high performance, capacity, and reliability is generally expensive, so multiple inexpensive non-volatile memories with low performance, capacity, and reliability are sometimes combined and used as backup memory. Non-volatile memory product cycles are shorter than storage systems, and successor products with the same performance and capacity may not be available. For this reason, backup memory is sometimes composed of multiple non-volatile memories with different performance and capacity.

[0004] For example, Patent Document 1 discloses a technique for increasing or decreasing cache capacity according to the amount of stored power in a battery in relation to saving data to a backup memory. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-182522 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the power supply to the storage system is interrupted in a state where any of the non-volatile memories constituting the backup memory fails, it may not be possible to save all of the data stored in the cache memory to the backup memory due to insufficient capacity of the backup memory or insufficient battery capacity caused by a longer backup time, which leaves the storage system in a vulnerable state until the failed non-volatile memory is replaced.

[0007] Although Patent Document 1 increases or decreases the cache capacity according to the amount of stored power in the battery, it does not take into consideration the backup of the data in the cache in the event that the non-volatile memory fails.

[0008] An object of the present disclosure is to provide a storage system, a cache control method and a program for the storage system that solve the above-mentioned problems. [Means for solving the problem]

[0009] A storage system according to one embodiment of the present disclosure includes a backup memory control means that, when a failed non-volatile memory is present in a backup memory composed of multiple non-volatile memories, calculates the amount of data that can be evacuated from a cache memory in non-volatile memory other than the failed non-volatile memory, and a cache control means that controls the amount of data written to the cache memory with the calculated data amount as an upper limit.

[0010] A cache control method in a storage system according to one embodiment of the present disclosure, when a backup memory consisting of multiple nonvolatile memories has a failed nonvolatile memory, calculates the amount of data that can be evacuated from a cache memory in nonvolatile memory other than the failed nonvolatile memory, and controls the amount of data written to the cache memory with the calculated data amount as an upper limit.

[0011] A program for a storage system according to one embodiment of the present disclosure causes a computer to execute the following steps when a backup memory consisting of multiple nonvolatile memories contains a failed nonvolatile memory: calculate the amount of data that can be evacuated from a cache memory in nonvolatile memory other than the failed nonvolatile memory, and control the amount of data written to the cache memory with the calculated amount of data as an upper limit. Effect of the Invention

[0012] According to the above aspect, even if a part or a plurality of non-volatile memories constituting the backup memory fail, it is possible to back up cache data while eliminating vulnerability of the storage system. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a storage system according to an embodiment of the present disclosure. [Diagram 2] 1 is a diagram showing the configuration of a storage system including values ​​related to the capacity and performance of each non-volatile memory. [Diagram 3] FIG. 13 is a diagram showing a flow of calculation of a cache capacity by a backup memory control unit. [Figure 4] FIG. 1 is a diagram illustrating an example of a configuration of a storage system according to an embodiment of the present disclosure. [Diagram 5] 2 is a block diagram showing an example of a hardware configuration of a controller of the storage system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment according to the present disclosure will be described with reference to the drawings. Note that the same or corresponding components in all the drawings are denoted by the same reference numerals, and common descriptions will be omitted.

[0015] 1 is a diagram showing the configuration of a storage system according to an embodiment of the present disclosure. The storage system (100) comprises a disk drive (110), a backup memory (120), a controller (140), a cache memory (150), and a battery (160). In addition, one or more hosts (170) that request reading and writing data from and to the storage system (100) are connected to the storage system (100) via a network or the like.

[0016] The disk drive (110) stores data written and read from the host (170). The disk drive (110) is composed of multiple disk drives (110) from the viewpoint of data integrity. The cache memory (150) is provided to improve processing speed, and temporarily stores data when a write request is received from the host (170). The backup memory (120) is a memory for saving data in the cache memory (150) in the event of a power outage in the storage system (100). The controller (140) controls the disk drive (110), the backup memory (120), and the cache memory (150), and performs processing for reading and writing data and for processing in the event of a power outage in the storage system (100). The battery (160) supplies power for saving data in the cache memory (150) to the backup memory (120) in the event of a power outage in the storage system (100).

[0017] The disk drive (110) is a large-capacity storage device such as a hard disk drive, a solid state drive (SSD), or a linear tape-open (LTO) drive.

[0018] The backup memory (120) is composed of multiple non-volatile memories (121, 122, 123). The non-volatile memories (121, 122, 123) may be composed of non-volatile memories with the same performance and capacity, or may be composed of non-volatile memories with different performance and capacity. Although Fig. 1 shows an example in which the backup memory (120) is composed of three non-volatile memories (121, 122, 123), the present invention is not limited to this example and may be composed of two or more non-volatile memories.

[0019] The controller (140) includes a cache control unit (141) and a backup memory control unit (142). In response to a write request from the host (170), the cache control unit (141) performs control for temporarily storing received data in the cache memory (150) and for saving data stored in the cache memory (150) in the disk drive (110). The backup memory control unit (142) monitors the state of the non-volatile memories (121, 122, 123) constituting the backup memory (120), and performs processing for optimally calculating the capacity of the reconstructed backup memory (120) in the event of a failure of the non-volatile memory, and notifying the cache control unit (141) of the calculated capacity.

[0020] The non-volatile memories (121, 122, 123) are configured with separate interfaces to the controller (140) so that they can operate in parallel. The backup memory control unit (142) can communicate with the non-volatile memories (121, 122, 123) individually via the interfaces to monitor their status.

[0021] Next, an overview of the operation of the storage system (100) when any of the non-volatile memories in the storage system (100) shown in Fig. 1 fails will be described. Here, a case where the non-volatile memory (121) fails will be described as an example.

[0022] In the storage system (100), when a failure occurs in the non-volatile memory (121) in the backup memory (120), the backup memory control unit (142) detects the failure of the non-volatile memory (121). The backup memory control unit (142) calculates the cache capacity that can be backed up in the backup memory (120) from the capacity and performance of the non-failed non-volatile memories (122, 123) in the backup memory (120) and the power capacity of the battery (160), and notifies the cache control unit (141).

[0023] The cache control unit (141), which has received notification of the new cache capacity from the backup memory control unit (142), reads data from the cache memory (150) and writes it to the disk drive (110), thereby reducing the amount of data written to the cache memory (150) until it is equal to or less than the notified new cache capacity. After the amount of data written to the cache memory (150) falls below the new cache capacity, the cache control unit (141) adjusts the amount of data written to the cache memory (150) so as not to exceed the new cache capacity. By controlling the amount of data stored in the cache memory (150) in this manner according to the state of the backup memory (120), it is possible to maintain the robustness of the storage system (100) even if the non-volatile memory constituting the backup memory (120) breaks down, and to back up data in the cache memory (150) when the power supply to the storage system (100) is interrupted.

[0024] Furthermore, when the failed non-volatile memory is repaired and replaced and restored to its original capacity, the backup memory control unit (142) calculates the cache capacity that can be backed up by the backup memory (120) from the capacity and performance of the available non-volatile memory, including the repaired and replaced non-volatile memory, and the power capacity of the battery (160), and notifies the cache control unit (141) again that the cache capacity has changed. The cache control unit (141) controls the amount of writing to the cache memory (150) using the new cache capacity notified again as an upper limit, by the same process as described above.

[0025] Next, we will explain the outline of the operation when calculating the cache capacity that can be backed up by the cache memory (150) while showing specific examples of the capacity and performance of the non-volatile memory that constitutes the backup memory (120). Figure 2 is a diagram showing the configuration of the storage system (200) including values ​​related to the capacity and performance of the non-volatile memory. The storage system (200), disk drive (210), backup memory (220), non-volatile memory (221, 222, 223), controller (240), cache control unit (241), backup memory control unit (242), cache memory (250), battery (260), and host (270) in FIG. 2 correspond to the storage system (100), disk drive (110), backup memory (120), non-volatile memory (121, 122, 123), controller (140), cache control unit (141), backup memory control unit (142), cache memory (150), battery (160), and host (170) in FIG. 1, respectively.

[0026] 2 shows an example of the backup memory (220) in which the nonvolatile memory (221) has a capacity of 200 GB and a throughput of 10 [GB / s], and the nonvolatile memories (222, 223) have a capacity of 120 GB and a throughput of 20 [GB / s]. That is, the nonvolatile memories (222, 223) have the same capacity / performance, and the nonvolatile memory (221) has a different capacity / performance from the nonvolatile memories (222, 223). Note that the throughput, which is the writing speed to the nonvolatile memory, is used as the performance of the nonvolatile memory. Also, the capacity of the cache memory (250) is 300 GB.

[0027] In the above-mentioned configuration of the storage system (200), an example of calculation of the amount of data that can be stored in the backup memory (220) will be described first, taking as an example a case where the non-volatile memory (221) constituting the backup memory (220) fails.

[0028] When the backup memory control unit (242) detects a failure in the nonvolatile memory (221), the backup memory control unit (242) starts calculating the amount of data that can be stored in the backup memory (220). In the example of Fig. 2, the available nonvolatile memories are the nonvolatile memory (222) and the nonvolatile memory (223). Here, it is assumed that the battery (260) stores power for 10 seconds as the amount of power that can be supplied when the battery (260) saves data in the cache memory (250) to the two nonvolatile memories (222, 223).

[0029] The backup memory control unit 242 calculates the upper limit of the storage capacity of the available non-volatile memory 222. To this end, the backup memory control unit 242 calculates the amount of data that can be transferred in 10 seconds of battery drive time, 200 GB (=20 [GB / s] x 10 [s]). Furthermore, as a result of comparing the upper limit of the capacity of the non-volatile memory 222, 120 GB, with the amount of data that can be transferred in 10 seconds of battery drive time, 200 GB, the backup memory control unit 242 calculates that 120 GB can be stored in the non-volatile memory 222.

[0030] Since the nonvolatile memory (222) and the nonvolatile memory (223) have the same capacity and performance, the backup memory control unit (242) calculates that 120 GB can be stored in the nonvolatile memory (223) as well. The backup memory control unit (242) calculates that the storage capacity of the backup memory (220) when configured with the nonvolatile memories (222, 223) is 240 GB (=120 GB + 120 GB). The backup memory control unit (242) notifies the cache control unit (241) of the new cache capacity of 240 GB, which is the result of this calculation. The cache control unit (241) limits writing to the cache memory (250) to an upper limit of the new cache capacity of 240 GB, which is less than the capacity of the cache memory (250) of 300 GB.

[0031] As another example, a case where the non-volatile memory (222) fails will be described. In this example, the battery (260) stores 10 seconds' worth of power as the amount of power that can be supplied when the data in the cache memory (250) is saved in the two non-volatile memories (221, 223). The backup memory control unit (242) determines that the available non-volatile memory (221) can store 200 GB of data, but that the amount of data that can be transferred during the 10-second power supply time from the battery (260) is 100 GB (=10 [GB / s] x 10 [s]) based on the throughput of the non-volatile memory (221). The backup memory control unit (242) also determines that the other available non-volatile memory (223) can transfer 200 GB (=20 [GB / s] x 10 [s]) of data, but that the amount of data that can be transferred is 120 GB, which is the upper limit of the capacity of the non-volatile memory (223). The backup memory control unit (242) then calculates the possible storage capacity of the backup memory (220) when configured with non-volatile memories (221, 223) to be 220 GB (=100 GB + 120 GB). The backup memory control unit (242) notifies the cache control unit (241) of the new cache capacity resulting from this calculation. The cache control unit (241) limits writing to the cache memory (250) to an upper limit of the new cache capacity of 220 GB, which is less than the capacity of the cache memory (250) of 300 GB.

[0032] 3 is a diagram showing a flow of calculation of the cache capacity in the backup memory (220) by the backup memory control unit (242). The flow of calculation of the cache capacity in the backup memory (220) by the backup memory control unit (242) will be described with reference to FIGS. 2 and 3.

[0033] The following describes a method for calculating the cache capacity when the backup memory is composed of n nonvolatile memories. Here, the nonvolatile memory (i) is the "i"th memory (i: an integer from 1 to n), and an initial value of "1" is set for the variable "i" before the start of step S12. In addition, the operation of the backup memory control unit (242) will be explained using the following parameters.

[0034] C: Cache capacity of cache memory B: Battery life Ci: Capacity of non-volatile memory (i) Pi: Throughput of non-volatile memory (i) CPi: The capacity that non-volatile memory (i) can save within the battery operating time (B) SVi: The amount of energy that can be saved during the time that non-volatile memory (i) can operate on battery power Cbup: When non-volatile memory fails, the capacity that can be saved by the backup memory excluding the failed non-volatile memory

[0035] First, the backup memory control unit (242) checks the number n of non-volatile memories implemented in the backup memory (220) by checking the presence or absence of non-volatile memory via an interface individually provided for each non-volatile memory (S11).

[0036] Next, the backup memory control unit 242 checks the status of the non-volatile memory (i) through an interface with the non-volatile memory (i) (S12). If the result of the status check is a "failure state", data cannot be saved in the non-volatile memory (i), and so the saveable capacity SVi of the non-volatile memory (i) is set to 0 (S13).

[0037] If the result of the status check is "normal", the backup memory control unit (242) acquires information on the storage capacity Ci and throughput Pi, which is the performance, of the nonvolatile memory (i) for the nonvolatile memory (i) (S14). The backup memory control unit (242) calculates the capacity CPi=PixB that the nonvolatile memory (i) can save within the battery operating time (B) from the acquired throughput Pi of the nonvolatile memory (i) (S15). Next, the backup memory control unit (242) compares the capacity CPi with the storage capacity Ci, and records the smaller one as the capacity SVi=min(CPi, Ci) that can be saved during the time that the nonvolatile memory (i) can operate on battery power (S16).

[0038] The backup memory control unit (242) determines whether the variable "i" matches the number n of non-volatile memories (S17). If they do not match (S17: No), the backup memory control unit (242) increments the variable "i" and proceeds to processing for the next non-volatile memory (S12).

[0039] If they match (S17: Yes), the backup memory control unit 242 calculates the capacity Cbup that can be saved during the time the backup memory 220 can operate on battery power by adding up SV1 to SVn (Cbup=ΣSVi) (S18).

[0040] If the capacity Cbup is smaller than the cache capacity C of the cache memory, the backup memory control unit (242) notifies the cache control unit (241) of the capacity Cbup as a new cache capacity (S19).

[0041] In this manner, the backup memory control unit 242 calculates the cache capacity in the backup memory 220. The flow for calculating the cache capacity shown in Fig. 3 is executed not only when a failure in the non-volatile memory is detected, but also when the storage system is started, when the non-volatile memory is replaced, and / or when the non-volatile memory is added or removed.

[0042] As described above, the storage system enables backup of cache data while maintaining robustness against power outages even if some or more of the non-volatile memories constituting the backup memory fail.

[0043] Furthermore, with the processing described in the present disclosure, even when non-volatile memories are mixed due to a change in generation, etc., by utilizing the excess capacity of normal non-volatile memory in the event of a non-volatile memory failure, the cache capacity that can be backed up can be maximized as much as possible, making it possible to minimize performance degradation due to a decrease in cache capacity.

[0044] Furthermore, if the backup non-volatile memory fails, the capacity of the cache memory that is the backup source is optimally limited according to the capacity and performance of the backup memory configured after the failure, thereby making it possible to perform backup even if the non-volatile memory fails.

[0045] Generally, batteries used during power outages are designed with a certain amount of storage capacity in mind, so it is possible to provide a large backup capacity that also takes into account the surplus storage capacity.

[0046] 4 is a diagram showing an example of the configuration of a storage system (100) according to an embodiment of the present disclosure. The storage system (100) includes a cache control unit (101) and a backup memory control unit (102). When a backup memory consisting of multiple nonvolatile memories has a failed nonvolatile memory, the backup memory control unit (102) calculates the amount of data that can be saved from the cache memory in the nonvolatile memory other than the failed nonvolatile memory. The cache control unit (101) controls the amount of data written to the cache memory, with the calculated amount of data set as an upper limit.

[0047] 5 is a block diagram showing an example of a hardware configuration of a controller (140) in a storage system (100). The hardware configuration of the controller (140) includes a CPU (11), a random access memory (RAM) (12), a read only memory (ROM) (13), and a storage device (14). The ROM (13) and the storage device (14) store programs and information that realize the functions of the controller (140). The RAM (12) is used as a working area for temporarily storing data and the like used by the CPU (11) during operation. The controller (140) also includes an input / output port (15) that serves as an interface with the disk drive (110), backup memory (120), cache memory (150), and the like. The input / output port (15) also functions as a communication port for communication connection with a host (170). The ROM (13) may be configured with an EEPROM (Electrically Erasable Programmable Read-Only Memory) or the like, and the recording device (14) may be configured with a hard disk, an SSD, or the like, and the computer program for realizing the functions of the controller (140) may be updated in the ROM (13) or the recording device (14).

[0048] Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the above-mentioned embodiments. Various modifications that can be understood by a person skilled in the art can be made to the configuration and details of the present disclosure within the scope of the present disclosure. Furthermore, each embodiment can be appropriately combined with other embodiments.

[0049] A part or all of the above-described embodiments may be described as, but is not limited to, the following supplementary notes.

[0050] (Appendix 1) a backup memory control means for calculating an amount of data that can be saved from the cache memory in the nonvolatile memory other than the failed nonvolatile memory when the backup memory is composed of a plurality of nonvolatile memories and the failed nonvolatile memory is present; a cache control means for controlling the amount of data written to the cache memory with the calculated amount of data set as an upper limit; A storage system comprising:

[0051] (Appendix 2) the backup memory control means determines the amount of data that can be saved in each of the non-volatile memories other than the failed non-volatile memory based on the capacity and performance of the non-volatile memories and the available battery operating time for saving the data in the cache memory to the backup memory when the power supply is interrupted; 2. The storage system of claim 1.

[0052] (Appendix 3) the backup memory control means determines, as the amount of data that can be saved in each of the nonvolatile memories other than the failed nonvolatile memory, the smaller of the capacity of the nonvolatile memory and a data transfer capacity calculated based on the performance of the nonvolatile memory and the available operation time of the battery; 3. The storage system of claim 2.

[0053] (Appendix 4) the backup memory control means sets the amount of data that can be saved in the failed non-volatile memory to zero. 4. The storage system of claim 3.

[0054] (Appendix 5) when the sum of the amounts of data that can be saved in each of the plurality of non-volatile memories falls below the capacity of the cache memory, the backup memory control means controls the amount of data written to the cache memory, with the calculated amount of data as an upper limit; 5. The storage system of claim 4.

[0055] (Appendix 6) The battery operation time of the battery is defined as the operation time available for data evacuation in all non-volatile memories other than the failed non-volatile memory. 6. A storage system according to any one of claims 2 to 5.

[0056] (Appendix 7) the backup memory control means and the cache control means are included in a controller, and each of the plurality of non-volatile memories has a separate interface with the controller; 7. A storage system according to any one of claims 1 to 6.

[0057] (Appendix 8) the backup memory control means calculates the amount of data that can be saved in the non-volatile memory when a failure is detected in any of the plurality of non-volatile memories, and also when the storage system is started, when the non-volatile memory is replaced, and / or when the non-volatile memory is added or removed; 8. A storage system according to any one of claims 1 to 7.

[0058] (Appendix 11) When a backup memory including a plurality of nonvolatile memories has a failed nonvolatile memory, an amount of data that can be evacuated from the cache memory is calculated in the nonvolatile memory other than the failed nonvolatile memory; controlling the amount of data written to the cache memory with the calculated amount of data as an upper limit; A cache control method in a storage system.

[0059] (Appendix 12) determining an amount of data that can be saved in each of the non-volatile memories other than the failed non-volatile memory based on the capacity and performance of the non-volatile memories and an available battery operating time for saving the data in the cache memory to the backup memory when the power supply is interrupted; A cache control method in the storage system according to claim 11.

[0060] (Appendix 13) the capacity of the non-volatile memory and a data transfer capacity calculated based on the performance of the non-volatile memory and the remaining operating time of the battery, whichever is smaller, are determined as the amount of data that can be saved in each of the non-volatile memories other than the failed non-volatile memory. A cache control method in the storage system according to claim 12.

[0061] (Appendix 14) The amount of data that can be saved in the failed non-volatile memory is set to zero. A cache control method in the storage system according to claim 13.

[0062] (Appendix 15) when the sum of the amounts of data that can be saved in each of the plurality of non-volatile memories falls below the capacity of the cache memory, the amount of data written to the cache memory is controlled with the calculated amount of data as an upper limit; A cache control method in the storage system according to claim 14.

[0063] (Appendix 16) The battery operation time of the battery is defined as the operation time available for data evacuation in all non-volatile memories other than the failed non-volatile memory. A cache control method in a storage system according to any one of claims 12 to 15.

[0064] (Appendix 17) The storage system includes a controller, and each of the plurality of non-volatile memories separately interfaces with the controller. A cache control method in a storage system according to any one of claims 11 to 16.

[0065] (Appendix 18) calculating an amount of data that can be saved in the non-volatile memory when a failure is detected in any of the plurality of non-volatile memories, when the storage system is started, when the non-volatile memory is replaced, and / or when the non-volatile memory is added or removed; A cache control method in the storage system according to any one of claims 11 to 17.

[0066] (Appendix 21) When a backup memory including a plurality of nonvolatile memories has a failed nonvolatile memory, an amount of data that can be evacuated from the cache memory is calculated in the nonvolatile memory other than the failed nonvolatile memory; controlling the amount of data written to the cache memory with the calculated amount of data as an upper limit; A program for a storage system that causes a computer to execute the following:

[0067] (Appendix 22) determining an amount of data that can be saved in each of the non-volatile memories other than the failed non-volatile memory based on the capacity and performance of the non-volatile memories and an available battery operating time for saving the data in the cache memory to the backup memory when the power supply is interrupted; 22. The program according to claim 21, which causes a computer to execute the steps.

[0068] (Appendix 23) the capacity of the non-volatile memory and a data transfer capacity calculated based on the performance of the non-volatile memory and the remaining operating time of the battery, whichever is smaller, are determined as the amount of data that can be saved in each of the non-volatile memories other than the failed non-volatile memory. 23. The program according to claim 22, which causes a computer to execute the steps.

[0069] (Appendix 24) The amount of data that can be saved in the failed non-volatile memory is set to zero. The program according to claim 23, which causes a computer to execute the steps.

[0070] (Appendix 25) when the sum of the amounts of data that can be saved in each of the plurality of non-volatile memories falls below the capacity of the cache memory, the amount of data written to the cache memory is controlled with the calculated amount of data as an upper limit; The program according to claim 24, which causes a computer to execute the steps.

[0071] (Appendix 26) The battery operation time of the battery is defined as the operation time available for data evacuation in all non-volatile memories other than the failed non-volatile memory. 26. A program according to any one of appendix 22 to appendix 25.

[0072] (Appendix 27) The storage system includes a controller, and each of the plurality of non-volatile memories separately interfaces with the controller. 27. A program according to any one of claims 21 to 26.

[0073] (Appendix 28) calculating an amount of data that can be saved in the non-volatile memory when a failure is detected in any of the plurality of non-volatile memories, when the storage system is started, when the non-volatile memory is replaced, and / or when the non-volatile memory is added or removed; A program according to any one of appendices 21 to 27, which causes a computer to execute the steps. [Explanation of symbols]

[0074] 100 Storage Systems 110 Disk Drive 120 Backup Memory 121,122,123 Non-volatile memory 140 Controller 141 Cache control unit 142 Backup memory control section 150 Cache Memory 160 Battery 170 Host

Claims

1. a backup memory control means for calculating an amount of data that can be saved from the cache memory in the nonvolatile memory other than the failed nonvolatile memory when the backup memory is composed of a plurality of nonvolatile memories and the failed nonvolatile memory is present; a cache control means for controlling the amount of data written to the cache memory with the calculated amount of data set as an upper limit; A storage system comprising:

2. the backup memory control means determines the amount of data that can be saved in each of the non-volatile memories other than the failed non-volatile memory based on the capacity and performance of the non-volatile memories and the available battery operating time for saving the data in the cache memory to the backup memory when the power supply is interrupted; The storage system according to claim 1 .

3. the backup memory control means determines, as the amount of data that can be saved in each of the nonvolatile memories other than the failed nonvolatile memory, the smaller of the capacity of the nonvolatile memory and a data transfer capacity calculated based on the performance of the nonvolatile memory and the available operation time of the battery; The storage system according to claim 2.

4. the backup memory control means sets the amount of data that can be saved in the failed non-volatile memory to zero. The storage system according to claim 3.

5. when the sum of the amounts of data that can be saved in each of the plurality of non-volatile memories falls below the capacity of the cache memory, the backup memory control means controls the amount of data written to the cache memory, with the calculated amount of data as an upper limit; The storage system according to claim 4.

6. The battery operation time of the battery is defined as the operation time available for data evacuation in all non-volatile memories other than the failed non-volatile memory. The storage system according to claim 2.

7. the backup memory control means and the cache control means are included in a controller, and each of the plurality of non-volatile memories has a separate interface with the controller; The storage system according to claim 1 .

8. the backup memory control means calculates the amount of data that can be saved in the non-volatile memory when a failure is detected in any of the plurality of non-volatile memories, and also when the storage system is started up, when the non-volatile memory is replaced, and / or when the non-volatile memory is added or removed; The storage system according to claim 1 .

9. When a backup memory including a plurality of nonvolatile memories has a failed nonvolatile memory, an amount of data that can be evacuated from the cache memory is calculated in the nonvolatile memory other than the failed nonvolatile memory; controlling the amount of data written to the cache memory with the calculated amount of data as an upper limit; A cache control method in a storage system.

10. When a backup memory including a plurality of nonvolatile memories has a failed nonvolatile memory, an amount of data that can be evacuated from the cache memory is calculated in the nonvolatile memory other than the failed nonvolatile memory; controlling the amount of data written to the cache memory with the calculated amount of data as an upper limit; A program for a storage system that causes a computer to execute the following:

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