Storage system, cache control method in storage system and program

Abstract

To provide a storage system that can back up cache data while eliminating vulnerability as the storage system even when a part or a plurality of nonvolatile memories constituting a backup memory fails.SOLUTION: A storage system includes a cache control unit and a backup memory control unit. When a backup memory constituted by multiple nonvolatile memories has a failed nonvolatile memory, the backup memory control unit calculates the amount of data that can be saved from a cache memory, in the nonvolatile memories other than the failed nonvolatile memory. The cache control unit controls a writing amount to the cache memory while setting the calculated amount of data as an upper limit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Advances in information technology have dramatically increased the amount of information handled. This has led to a growing need for high-capacity, high-density storage systems. Data handling in these storage systems is generally managed by a file system. Data must be written to a disk drive, but to ensure performance, temporary processing is performed using cache memory installed within the storage, including the disk drive. If the power supply is interrupted when using cache memory, the data in the cache memory may be lost. For this reason, it is common to install batteries in storage systems and back up data to non-volatile memory to prevent data loss.

[0003] Non-volatile memory with high performance, capacity, and reliability is generally expensive, so backup memory is sometimes made up of multiple inexpensive non-volatile memories with low performance, capacity, and reliability. The product cycle for non-volatile memory is shorter than that of storage systems, and successor products with the same performance and capacity may not be available. For this reason, backup memory is sometimes made up 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] Japanese Patent Application Publication No. 2017-182522 Summary of the Invention [Problem to be solved by the invention]

[0006] However, if one of the nonvolatile memories that make up the backup memory fails and the power supply to the storage system is interrupted, it may become impossible 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 an extended backup time, which leaves the storage system vulnerable until the failed nonvolatile 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 backing up the data in the cache in the event that the nonvolatile memory fails.

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

[0009] A storage system according to one aspect of the present disclosure includes a backup memory control means that, 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 a nonvolatile memory other than the failed nonvolatile memory, and a cache control means that controls the amount of data written to the cache memory with the calculated amount of data as an upper limit.

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

[0011] A program for a storage system according to one aspect of the present disclosure causes a computer to execute the following steps: when a backup memory consisting of multiple nonvolatile memories has a failed nonvolatile memory, calculate the amount of data that can be evacuated from the cache memory in the 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. [Effects of the Invention]

[0012] According to the above aspect, even if a part or a plurality of nonvolatile memories constituting the backup memory fail, it is possible to back up cache data while eliminating vulnerability of the storage system. [Brief explanation 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. [Figure 2] FIG. 10 is a diagram showing the configuration of a storage system including values ​​related to the capacity and performance of each nonvolatile memory. [Figure 3] FIG. 10 is a diagram showing a flow of calculation of cache capacity by a backup memory control unit. [Figure 4] FIG. 1 is a diagram illustrating an example of the configuration of a storage system according to an embodiment of the present disclosure. [Figure 5] FIG. 2 is a block diagram showing an example of a hardware configuration of a controller in a storage system. DETAILED DESCRIPTION OF THE INVENTION

[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). The storage system (100) is also connected to one or more hosts (170) via a network or the like, which requests data to be read or written from or to the storage system (100).

[0016] The disk drive (110) stores data written and read from the host (170). The disk drive (110) is configured with multiple disk drives (110) to ensure data integrity. The cache memory (150) is provided to improve processing speed and temporarily stores write 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), backup memory (120), and cache memory (150) and performs data read / write operations and processing in the event of a power outage in the storage system (100). The battery (160) supplies power to save 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 nonvolatile memories (121, 122, 123). These nonvolatile memories (121, 122, 123) may be composed of nonvolatile memories with the same performance and capacity, or may be composed of nonvolatile memories with different performance and capacity. While FIG. 1 shows an example in which the backup memory (120) is composed of three nonvolatile memories (121, 122, 123), this is not limiting and the backup memory (120) may be composed of two or more nonvolatile 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 to temporarily store received data in the cache memory (150) and to save the data stored in the cache memory (150) in the disk drive (110). The backup memory control unit (142) monitors the status of the nonvolatile memories (121, 122, 123) that constitute the backup memory (120), and, in the event of a failure of the nonvolatile memory, performs processing to optimally calculate the capacity of the reconstructed backup memory (120) and notify the cache control unit (141) of the calculated capacity.

[0020] The nonvolatile memories (121, 122, 123) are configured with individual interfaces with the controller (140) so that they can operate in parallel. The backup memory control unit (142) can communicate with the nonvolatile 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 a failure occurs in any of the nonvolatile memories in the storage system (100) shown in Fig. 1 will be described. Here, the case where the nonvolatile memory (121) fails will be described as an example.

[0022] In the storage system (100), when a nonvolatile memory (121) in the backup memory (120) fails, the backup memory control unit (142) detects the failure of the nonvolatile 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 nonvolatile memories (122, 123) in the backup memory (120) and the power capacity of the battery (160), and notifies the cache control unit (141).

[0023] Upon receiving notification of the new cache capacity from the backup memory control unit (142), the cache control unit (141) 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 that it does not 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), the robustness of the storage system (100) is maintained even if the nonvolatile memory constituting the backup memory (120) fails, and data in the cache memory (150) can be backed up when the power supply to the storage system (100) is interrupted.

[0024] Furthermore, when the failed nonvolatile 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) based on the capacity and performance of the available nonvolatile memory, including the repaired and replaced nonvolatile 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 notified new cache capacity 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 nonvolatile memory that makes up 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 nonvolatile 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] In FIG. 2, the backup memory (220) is shown as an example 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. In other words, this shows an example in which the nonvolatile memories (222, 223) have the same capacity and performance, and the nonvolatile memory (221) has a different capacity and performance than the nonvolatile memories (222, 223). Note that the performance of the nonvolatile memory is represented by the throughput, which is the write speed to the nonvolatile memory. In addition, this example shows a cache memory (250) with a capacity of 300 GB.

[0027] In the configuration of the storage system (200) as described above, an example of calculating the amount of data that can be stored in the backup memory (220) will be explained first, taking as an example a case where the nonvolatile memory (221) that constitutes 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 a 10-second amount of power as the amount of power that can be supplied when the data in the cache memory 250 is saved in the two nonvolatile memories 222 and 223.

[0029] The backup memory control unit 242 calculates the upper limit of the storage capacity of the available nonvolatile 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-operated time as 200 GB (= 20 [GB / s] x 10 [s]). Furthermore, the backup memory control unit 242 compares the upper limit of the capacity of the nonvolatile memory 222, 120 GB, with the amount of data that can be transferred in 10 seconds of battery-operated time as 200 GB, and calculates that 120 GB can be stored in the nonvolatile memory 222.

[0030] Because 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 also be stored in the nonvolatile memory (223). 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 nonvolatile 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 backing up data from the cache memory 250 to the two nonvolatile memories 221 and 223. The backup memory control unit 242 determines that the available nonvolatile memory 221 has a storage capacity of 200 GB, 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 nonvolatile memory 221. The backup memory control unit 242 also determines that the other available nonvolatile memory 223 has a data transfer rate of 200 GB (= 20 GB / s x 10 s), but that the storage capacity is limited to 120 GB, which is the upper limit of the capacity of the nonvolatile memory 223. The backup memory control unit 242 then calculates the storage capacity of the backup memory 220 when configured with nonvolatile memories 221, 223 as 220 GB (= 100 GB + 120 GB). The backup memory control unit 242 notifies the cache control unit 241 of the new cache capacity obtained by this calculation. The cache control unit 241 limits writing to the cache memory 250 to a new cache capacity of 220 GB, which is equal to or less than the capacity of the cache memory 250 of 300 GB.

[0032] 3 is a diagram showing the 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.

[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 the initial value of the variable "i" is set to "1" before the start of step S12. 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 storage 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 nonvolatile memory (i) via the interface with the nonvolatile memory (i) (S12). If the result of the status check is a "failure state," data cannot be saved to the nonvolatile memory (i), and therefore the saveable capacity SVi of the nonvolatile 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 regarding the storage capacity Ci of the nonvolatile memory (i) and the throughput Pi, which represents its performance, 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 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 nonvolatile 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 nonvolatile 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 that 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 the new cache capacity (S19).

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

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

[0043] Furthermore, with the processing described in this 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, it is possible to maximize the cache capacity that can be backed up as much as possible, thereby minimizing performance degradation due to a decrease in cache capacity.

[0044] Furthermore, if the backup nonvolatile memory fails, the capacity of the cache memory that serves as 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 nonvolatile memory fails.

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

[0046] 4 is a diagram illustrating an example 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 memories 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 as an upper limit.

[0047] 5 is a block diagram showing an example of the hardware configuration of the controller 140 in the storage system 100. The hardware configuration of the controller 140 includes a CPU 11, a RAM (Random Access Memory) 12, a ROM (Read Only Memory) 13, and a storage device 14. The ROM 13 and the storage device 14 store programs and information that implement the functions of the controller 140. The RAM 12 is used as a work area for temporarily storing data used by the CPU 11 and other components 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 other components. The input / output port 15 also functions as a communication port for communication with the 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, so that the computer program for realizing the functions of the controller (140) can 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-described embodiments. Various modifications that can be understood by those 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 combined with other embodiments as appropriate.

[0049] Some or all of the above-described embodiments can be described as, but are not limited to, the following supplementary notes.

[0050] (Appendix 1) a backup memory control means for calculating, when a backup memory including a plurality of nonvolatile memories has a failed nonvolatile memory, an amount of data that can be saved from the cache memory in the nonvolatile memories other than the failed nonvolatile memory; a cache control means for controlling the amount of data written to the cache memory with the calculated amount of data 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 nonvolatile memories other than the failed nonvolatile memory based on the capacity and performance of the nonvolatile memories and the available battery operating time for saving the data in the cache memory to the backup memory when power supply is interrupted; 2. The storage system of claim 1.

[0052] (Appendix 3) the backup memory control means determines the smaller of the capacity of the nonvolatile memory and a data transfer capacity determined based on the performance of the nonvolatile memory and the remaining battery life as the amount of data that can be saved in each of the nonvolatile memories other than the failed nonvolatile memory; 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 nonvolatile memory to zero. 4. The storage system of claim 3.

[0054] (Appendix 5) 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, when the total amount of data that can be saved in each of the plurality of nonvolatile memories is less than the capacity of the cache memory; 5. The storage system of claim 4.

[0055] (Appendix 6) The battery operating time of the battery is defined as the operating time available for data evacuation in all nonvolatile memories other than the failed nonvolatile memory. 6. The storage system according to any one of Supplementary Note 2 to Supplementary Note 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 nonvolatile memories has a separate interface with the controller; 7. The 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 nonvolatile memory when a failure is detected in any of the plurality of nonvolatile memories, when the storage system is started, when the nonvolatile memory is replaced, and / or when the nonvolatile memory is added or removed; 8. The storage system according to any one of claims 1 to 7.

[0058] (Appendix 11) When a backup memory configured with a plurality of nonvolatile memories has a failed nonvolatile memory, the amount of data that can be saved from the cache memory is calculated in the nonvolatile memories 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 the amount of data that can be saved in each of the nonvolatile memories other than the failed nonvolatile memory from the capacity and performance of the nonvolatile 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; A cache control method in the storage system according to claim 11.

[0060] (Appendix 13) the capacity of the nonvolatile memory and the data transfer capacity calculated based on the performance of the nonvolatile memory and the remaining battery life, whichever is smaller, are set as the amount of data that can be saved in each of the nonvolatile memories other than the failed nonvolatile 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 nonvolatile 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 data amounts that can be saved in each of the plurality of nonvolatile memories is less than the capacity of the cache memory, the amount of data written to the cache memory is controlled with the calculated data amount as an upper limit. A cache control method in the storage system according to claim 14.

[0063] (Appendix 16) The battery operating time of the battery is defined as the operating time available for data evacuation in all nonvolatile memories other than the failed nonvolatile memory. A cache control method in the storage system according to any one of Supplementary Note 12 to Supplementary Note 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 the storage system according to any one of Supplementary Note 11 to Supplementary Note 16.

[0065] (Appendix 18) calculates the amount of data that can be saved in the nonvolatile memories when a failure of any of the nonvolatile memories is detected, when the storage system is started, when the nonvolatile memories are replaced, and / or when the nonvolatile memories are added or removed; A cache control method in the storage system according to any one of Supplementary Note 11 to Supplementary Note 17.

[0066] (Appendix 21) When a backup memory configured with a plurality of nonvolatile memories has a failed nonvolatile memory, the amount of data that can be saved from the cache memory is calculated in the nonvolatile memories 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 the amount of data that can be saved in each of the nonvolatile memories other than the failed nonvolatile memory from the capacity and performance of the nonvolatile 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; 22. The program according to claim 21, which causes a computer to execute the steps.

[0068] (Appendix 23) the capacity of the nonvolatile memory and the data transfer capacity calculated based on the performance of the nonvolatile memory and the remaining battery life, whichever is smaller, are set as the amount of data that can be saved in each of the nonvolatile memories other than the failed nonvolatile 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 nonvolatile memory is set to zero. 24. The program according to claim 23, which causes a computer to execute the steps.

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

[0071] (Appendix 26) The battery operating time of the battery is defined as the operating time available for data evacuation in all nonvolatile memories other than the failed nonvolatile memory. 26. A program according to any one of appendices 22 to 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 appendices 21 to 26.

[0073] (Appendix 28) calculates the amount of data that can be saved in the nonvolatile memories when a failure of any of the nonvolatile memories is detected, when the storage system is started, when the nonvolatile memories are replaced, and / or when the nonvolatile memories are added or removed; 28. A program according to any one of appendices 21 to 27, which causes a computer to execute the following: [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 unit 150 cache memory 160 Battery 170 hosts

Claims

1. a backup memory control means for calculating, when a backup memory including a plurality of nonvolatile memories has a failed nonvolatile memory, an amount of data that can be saved from the cache memory in the nonvolatile memories other than the failed nonvolatile memory; a cache control means for controlling the amount of data written to the cache memory with the calculated amount of data 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 nonvolatile memories other than the failed nonvolatile memory based on the capacity and performance of the nonvolatile memories and the available battery operating time for saving the data in the cache memory to the backup memory when power supply is interrupted; The storage system according to claim 1 .

3. the backup memory control means determines the smaller of the capacity of the nonvolatile memory and a data transfer capacity determined based on the performance of the nonvolatile memory and the remaining battery life as the amount of data that can be saved in each of the nonvolatile memories other than the failed nonvolatile memory; 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 nonvolatile memory to zero. The storage system according to claim 3 .

5. 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, when the total amount of data that can be saved in each of the plurality of nonvolatile memories is less than the capacity of the cache memory; The storage system according to claim 4 .

6. The battery operating time of the battery is defined as the operating time available for data evacuation in all nonvolatile memories other than the failed nonvolatile 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 nonvolatile 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 nonvolatile memory when a failure is detected in any of the plurality of nonvolatile memories, when the storage system is started, when the nonvolatile memory is replaced, and / or when the nonvolatile memory is added or removed; The storage system according to any one of claims 1 to 7.

9. When a backup memory configured with a plurality of nonvolatile memories has a failed nonvolatile memory, the amount of data that can be saved 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 configured with a plurality of nonvolatile memories has a failed nonvolatile memory, the amount of data that can be saved 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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