Storage system having function to backup data in cache memory

• US 20090055590A1
• Filed: 02/05/2008
• Published: 02/26/2009
• Est. Priority Date: 08/22/2007
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Takahashi, Hideaki
• Granted Patent: US 8,261,032 B2
• Time in Patent Office: Days
• US Class Current: 711/119
• CPC Class Codes: G06F 11/1441 Resetting or repowering
• CPC Class Codes: G06F 11/2015 Redundant power supplies power supply failure G06F1/30
• CPC Class Codes: G06F 12/0804 with main memory updating G06F12/0806 takes precedence
• CPC Class Codes: G06F 12/0866 for peripheral storage systems, e.g. disk cache
• CPC Class Codes: Y02D 10/00 Energy efficient computing, e.g. low power processors, power management or thermal management

Abstract

A storage system comprises a plurality of control modules having a plurality of cache memories respectively. One or more dirty data elements out of a plurality of dirty data elements stored in a first cache memory in a first control module are copied to a second cache memory in a second control module. The one or more dirty data elements stored in the second cache memory are backed up to a non-volatile storage resource. The dirty data elements backed up from the first cache memory to the non-volatile storage resource are dirty data elements other than the one or more dirty data elements of which copying has completed, out of the plurality of dirty data elements.

Claims

1. A storage system, comprising:

a plurality of control modules for receiving I/O commands sent from a host device;

a plurality of storage devices for storing data according to I/O commands from the host device; and

a non-volatile storage resource which serves as the plurality of storage devices or another kind of non-volatile storage device, wherein

each control module comprises a cache memory and a control unit, and the control unit writes data according to an I/O command from the host device to the cache memory, and writes the data written in the cache memory to at least one of the plurality of storage devices or sends the data to the host device,

a first control unit in a first control module, out of the plurality of control modules, instructs a second control unit in a second control module out of the plurality of control modules to copy one or more dirty data elements out of a plurality of dirty data elements, which are stored in a first cache memory in the first control module and have not yet been written in the storage device,

the second control unit writes the one or more dirty data elements to a second cache memory in the second control module in response to the copy instruction, and backs up the one or more dirty data elements from the second cache memory to the non-volatile storage resource, and

the first control unit backs up dirty data elements, other than the one or more dirty data elements of which copying has completed from among the plurality of dirty data elements, from the first cache memory to the non-volatile storage resource.

2. The storage system according to claim 1, further comprising a plurality of power supply modules, which are power supplies of the plurality of control modules respectively, wherein

the number of the second control modules is the number of the first control modules or more, and one or more second control modules are provided for one first control module,

the non-volatile storage resource serves as a plurality of non-volatile memory modules of the plurality of control modules respectively,

each of the control modules further comprises a connection unit for communicably connecting the cache memory and the control unit,

the control modules are interconnected by the interconnection of the control units,

each power supply module includes a battery and a primary power supply,

the primary power supply supplies power to the cache memory and the control unit, and the battery supplies power to the cache memory and the control unit when power from the primary power supply stops,

the first control unit receives I/O commands from the host device while power is being supplied from the primary power supply, and if the received I/O command is a write command, then the first control unit writes a data element according to the write command to the first cache memory, creates management information to indicate a cache area, where a dirty data element exists, of the first cache memory and to indicate a control module to which the dirty data element is copied, and writes the information to the first cache memory, sends an instruction to copy one or more dirty data elements out of the plurality of dirty data elements to the second control unit via two or more connection units including a first connection unit of the first control module and a second connection unit of the second control module, then if a plurality of new dirty data elements exist in the first cache memory because of a plurality of data elements according to one or more write commands being written to the first cache memory, the first control unit sends an instruction to copy one or more dirty data elements out of the new plurality of dirty data elements to the second control unit via the two or more connection units, and updates the management information as copying of the dirty data elements completes,

while power is being supplied from the battery after the power supply from the primary power supply stops, the second control unit backs up the dirty data elements written in the second cache memory to the second non-volatile memory module of the second control module, stages the dirty data elements from the second non-volatile memory module to the second cache memory when power supply is restarted, and sends an instruction to copy the staged dirty data elements to the first control unit via the two or more connection units in parallel with the staging, and

while power is being supplied from the battery after power supply from the primary power supply stops, the first control unit backs up dirty data elements, other than the one or more dirty data elements of which copying has completed, and the management information from the first cache memory to the first non-volatile memory module of the first control module, and stages the management information and dirty data elements from the first non-volatile memory module to the first cache memory when power supply is restarted, and writes the dirty data elements staged in the second cache memory to the first cache memory according to the instruction of copying.

3. The storage system according to claim 2, wherein

a control module having a cache memory of which a consumption ratio, which is a ratio of the total amount of dirty data elements to a storage capacity of the cache memory, is a first predetermined ratio or more, becomes the first control module, and

a control module having a cache memory of which the consumption ratio is less than a second predetermined ratio becomes the second control module.

4. The storage system according to claim 2, wherein

the first control unit, when a write command is received from the host device and if a consumption ratio of the first cache memory is a third predetermined ratio or more, sends one or more data elements according to the write command to another control module via two or more connection units including a connection unit in the other control module and the first connection unit, and another control unit in the other control module writes the one or more data elements to a cache memory in the other control module.

5. The storage system according to claim 2, wherein

two or more storage devices out of the plurality of storage devices are assigned to each control module respectively,

each logical volume is formed based on the two or more storage devices, and each logical volume is a logical volume of which each control module is in-charge, and

when the first control unit receives a write command from the host device and if an open status of assigned logical volume for the first control unit itself, specified by the write command, is worse than a predetermined status, then the first control unit sends one or more data elements according to the write command to the other control module via two or more connection units including a connection unit of the other control module and the first connection unit, another control unit in the other control module writes the one or more data elements to a cache memory in the other control module, and writes the one or more data elements written in the cache memory to a logical volume assigned to the other control module.

6. The storage system according to claim 1, further comprising a power supply module including a primary power supply and a battery, wherein

the first control unit sends an instruction to copy the one or more dirty data elements while receiving the power supply from the primary power supply, and if the power supply from the primary power supply stops and power is received from the battery, the first control unit backs up dirty data elements other than the one or more dirty data elements of which copying has completed, out of the plurality of dirty data elements, from the first cache memory to the non-volatile storage resource without sending the instruction of copying.

7. The storage system according to claim 6, wherein a plurality of the power supply modules exist, and the plurality of power supply modules are power supplies for the plurality of control modules respectively.

8. The storage system according to claim 1, wherein

a control module having a cache memory of which a consumption ratio, which is a ratio of the total amount of dirty data elements to the storage capacity of the cache memory, is a first predetermined ratio or more, becomes the first control module,

a control module having a cache memory of which the consumption ratio is less than a second predetermined ratio, becomes the second control module, and

the number of the second control modules is the number of the first control modules or more, and one or more second control modules are provided to one first control module.

9. The storage system according to claim 1, wherein

each of the control modules further comprises a connection unit for communicably connecting the cache memory and the control unit, and

control modules are interconnected by the interconnection of the connection units.

10. The storage system according to claim 9, wherein

the first control unit, when a write command is received from the host device and if the consumption ratio of the first cache memory is a third predetermined ratio or more, sends one or more data elements according to the write command to another control module via two or more connection units including a connection unit in the other control module and the first connection unit, and the other control unit in the other control module writes the one or more data elements to a cache memory in the other control module.

11. The storage system according to claim 9, wherein

two or more storage devices out of the plurality of storage devices are assigned to each control module respectively,

each logical volume is formed based on the two or more storage devices, and each logical volume is a logical volume of which each control module is in-charge, and

when the first control unit receives a write command from the host device and if an open status of the assigned logical volume for the first control unit itself, specified by the write command, is worse than a predetermined status, then the first control unit sends one or more data elements according to the write command to another control module via two or more connection units including a connection unit in the other control module and the first connection unit, another control unit in the other control module writes the one or more data elements to a cache memory in the other control module, and writes the one or more data elements written in the cache memory to a logical volume assigned to the other control module.

12. The storage system according to claim 1, wherein

the first control unit creates management information to indicate a cache area, where a dirty data element exists, of the first cache memory and to indicate a control module to which the dirty data element is copied, and writes the information to the first cache memory, updates the management information as copying of the dirty data elements completes, and backs up the dirty data elements other than the one or more dirty data elements of which copying has completed and the management information from the first cache memory to the non-volatile storage resource.

13. The storage system according to claim 12, wherein

the first control unit receives I/O commands from the host device, and if the received I/O command is a write command, the first control unit writes a data element according to the write command to the first cache memory, sends the instruction to copy the one or more dirty data elements, then if a new plurality of dirty data elements exist in the first cache memory because a plurality of data elements according to one or more write commands are written in the first cache memory, the first control unit sends an instruction to copy one or more dirty data elements out of the plurality of new dirty data elements to the second control module.

14. The storage system according to claim 12, wherein

the second control unit backs up the dirty data elements copied in the second cache memory to the non-volatile storage resource, stages the dirty data elements from the non-volatile storage resource to the second cache memory, and sends an instruction to copy the staged dirty data elements to the first control module in parallel with the staging, and

the first control unit stages the management information and dirty data elements from the non-volatile storage resource to the first cache memory, and writes the dirty data elements from the second control module to the first cache memory in response to the instruction of copying.

15. The storage system according to claim 2, wherein the first control unit evenly divides the plurality of dirty data elements according to the total of the number of the first control modules, and the number of the second control modules, where one or more is/are provided for the first control modules.

16. A method for backing up data stored in a cache memory, which is performed in a storage system for temporarily storing data from a host device to a cache memory and then writing the data to a storage device,

the method comprising steps of:

copying one or more dirty data elements out of a plurality of dirty data elements, which have not yet been written in the storage device and are stored in a first cache memory in a first control module out of a plurality of control modules having a plurality of cache memories respectively, to a second cache memory in a second control module out of the plurality of control modules;

backing up the one or more dirty data elements from the second cache memory to a non-volatile storage resource, which is a storage device or another kind of non-volatile storage device; and

backing up the dirty data elements other than the one or more dirty data elements of which copying has completed out of the plurality of dirty data elements from the first cache memory to the non-volatile storage resource.

17. The method according to claim 16, wherein

the one or more dirty data elements are copied to the second cache memory while power is being supplied from a primary power supply, and dirty data elements other than the one or more dirty data elements, of which copying has completed, are backed up from the first cache-memory to the non-volatile storage resource, and the one or more dirty data elements, of which copying has completed, are backed up from the second cache memory to the non-volatile storage resource when the power supply from the primary power supply stops and power is supplied from a battery.

18. The method according to claim 17, wherein

if power is supplied again after the battery runs down, the dirty data elements are staged from the non-volatile storage resource to the first cache memory, and the dirty data elements are staged from the non-volatile storage resource to the second cache memory, and the dirty data elements are copied from the second cache memory to the first cache memory in parallel with the staging.

19. The method according to claim 18, wherein

the first control module creates management information to indicate a cache area, where a dirty data element exists, of the first cache memory and to indicate a control module to which the dirty data element is copied in the control module, and writes the information to the first cache memory, updates the management information as copying of the dirty data element completes, and for backup, the management information, in addition to the dirty data element, is backed up from the first cache memory to the non-volatile storage resource, and when power supply is restarted, the management information, in addition to the dirty data element, is staged from the non-volatile storage resource to the first cache memory.

20. The method according to claim 16, wherein the plurality of dirty data elements are evenly divided according to the total of the number of the first control modules and the number of the second control modules provided where one or more is/are provided for the first control modules.