Method and System for Migrating Data Between Flash Memory Devices

• US 20150067244A1
• Filed: 08/27/2014
• Published: 03/05/2015
• Est. Priority Date: 09/03/2013
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: Sandisk Technologies Incorporated (Western Digital Corporation)
• Inventors: Kruger, Warren Fritz
• Granted Patent: US 9,519,577 B2
• Time in Patent Office: Days
• US Class Current: 711/103
• CPC Class Codes: G06F 11/004 Error avoidance G06F11/07 and subgroups take precedence
• CPC Class Codes: G06F 11/1451 by selection of backup contents
• CPC Class Codes: G06F 11/1456 Hardware arrangements for backup
• CPC Class Codes: G06F 11/1458 Management of the backup or restore process
• CPC Class Codes: G06F 11/1612 where the redundant component is persistent storage
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 2201/81 Threshold
• CPC Class Codes: G06F 2212/1032 Reliability improvement, data loss prevention, degraded operation etc
• CPC Class Codes: G06F 2212/1044 Space efficiency improvement
• CPC Class Codes: G06F 2212/7204 Capacity control, e.g. partitioning, end-of-life degradation
• CPC Class Codes: G06F 2212/7208 Multiple device management, e.g. distributing data over multiple flash devices
• CPC Class Codes: G06F 3/0689 Disk arrays, e.g. RAID, JBOD

Abstract

The embodiments described herein include systems, methods and/or devices that may enhance the endurance of a storage system including a storage medium. The method includes: dividing a plurality of flash memory devices into logical chunks each logical chunk including one or more flash memory blocks; and detecting a trigger condition with respect to a respective flash memory device of the plurality of flash memory devices. In response to detecting the trigger condition, the method includes: selecting one of the logical chunks of the respective flash memory device for migration in accordance with predefined selection criteria; and storing a replicated logical chunk, comprising a copy of the selected logical chunk, at a second flash memory device. The method includes: remapping an address of the selected logical chunk to a physical location of the replicated logical chunk; and decreasing a number of logical chunks associated with the respective flash memory device.

Claims

1. A method of managing a storage system that comprises a storage controller and a plurality of flash memory devices, each with a plurality of flash memory blocks, the method comprising:

at the storage controller;

dividing each of the plurality of flash memory devices into a plurality of logical chunks, wherein each logical chunk includes one or more flash memory blocks;

detecting a predefined trigger condition with respect to a respective flash memory device of the plurality of flash memory devices;

in response to detecting the predefined trigger condition;

selecting one of the plurality of logical chunks of the respective flash memory device for migration in accordance with predefined selection criteria;

storing a replicated logical chunk, comprising a copy of the selected logical chunk, at a second flash memory device different from the respective flash memory device; and

remapping an address of the selected logical chunk to a physical location of the replicated logical chunk; and

decreasing a number of logical chunks associated with the respective flash memory device.

2. The method of claim 1, wherein the second flash memory device is in a different failure domain than the respective flash memory device.

3. The method of claim 1, wherein the detected predefined trigger condition is one of a set of a predefined trigger conditions.

4. The method of claim 1, wherein the storage controller detects the predefined trigger condition after directing a memory access request to the respective flash memory device.

5. The method of claim 1, further comprising

in response to detecting the predefined trigger condition, querying the respective flash memory device to determine whether the size of the respective flash memory device is smaller than a previous size of the respective flash memory device;

and

wherein the selecting and storing are performed in accordance with a determination that the query indicates that the size of the respective flash memory device is smaller than the previous size of the respective flash memory device.

6. The method of claim 1, wherein the predefined trigger condition indicates that a counter of failed flash memory blocks for the respective flash memory device exceeds an integer multiple of a threshold number, the threshold number comprising the number of flash memory blocks included in a logical chunk or an integer multiple of the number of flash memory blocks included in a logical chunk.

7. The method of claim 1, wherein the logical chunks are allocated for storing data and are organized into a plurality of redundancy sets, each redundancy set comprising one or more logical chunks and storing redundant data sufficient to enable recovery of data stored in at least one of the one or more logical chunks.

8. The method of claim 7, wherein the replicated logical chunk is included in a respective redundancy set of the plurality of redundancy sets that formerly included the selected logical chunk.

9. The method of claim 7, wherein a respective redundancy set of the plurality of redundancy sets is a contiguous stripe across the plurality of flash memory devices, and wherein the replicated logical chunk is stored in a same contiguous stripe as the selected logical chunk at the second flash memory device different from the respective flash memory device.

10. The method of claim 7, wherein the replicated logical chunk is stored in accordance with a preferred storage utilization scheme, the method including, associating the replicated logical chunk with a respective redundancy set of the plurality of redundancy sets in an indirection table.

11. The method of claim 1, wherein the predefined selection criteria include a least utilized logical chunk or least populated logical chunk of the respective flash memory device.

12. The method of claim 1, wherein the predefined selection criteria include the logical chunk associated with a memory access request.

13. The method of claim 1, wherein a size of the plurality of logical chunks is predetermined by software.

14. The method of claim 1, wherein a size of the plurality of logical chunks is determined based on a protocol used by the storage system.

15. The method of claim 1, further comprising:

in response to detecting the predefined trigger condition with respect to the respective flash memory device, re-encoding data in at least one logical chunk of the respective flash memory device with a higher level of error correction protection than a prior encoding of the data in the at least one logical chunk of the respective flash memory device.

16. A storage controller, comprising:

one or more processors;

a host interface configured to couple the storage controller to a host;

a storage medium interface configured to couple the storage controller to a storage medium including a plurality of flash memory devices, each with a plurality of flash memory blocks; and

a storage controller memory storing instructions, which, when executed by the one or more processors, causes the storage controller to perform operations comprising;

dividing each of the plurality of flash memory devices into a plurality of logical chunks, wherein each logical chunk includes one or more flash memory blocks;

detecting a predefined trigger condition with respect to a respective flash memory device of the plurality of flash memory devices;

in response to detecting the predefined trigger condition;

selecting one of the plurality of logical chunks of the respective flash memory device for migration in accordance with predefined selection criteria; and

storing a replicated logical chunk, comprising a copy of the selected logical chunk, at a second flash memory device different from the respective flash memory device; and

remapping an address of the selected logical chunk to a physical location of the replicated logical chunk; and

decreasing a number of logical chunks associated with the respective flash memory device.

17. The storage controller of claim 16, wherein the logical chunks are allocated for storing data and are organized into a plurality of redundancy sets, each redundancy set comprising one or more logical chunks and storing redundant data sufficient to enable recovery of data stored in at least one of the one or more logical chunks.

18. The storage controller of claim 17, wherein the replicated logical chunk is included in a respective redundancy set of the plurality of redundancy sets that formerly included the selected logical chunk.

19. The storage controller of claim 17, wherein a respective redundancy set of the plurality of redundancy sets is a contiguous stripe across the plurality of flash memory devices, and wherein the replicated logical chunk is stored in a same contiguous stripe as the selected logical chunk at the second flash memory device different from the respective flash memory device.

20. The storage controller of claim 17, wherein the replicated logical chunk is stored in accordance with a preferred storage utilization scheme, the method including, associating the replicated logical chunk with a respective redundancy set of the plurality of redundancy sets in an indirection table.

21. A non-transitory computer readable storage medium, storing one or more programs for execution by one or more processors of a storage controller coupled to a storage medium including a plurality of flash memory devices, wherein each flash memory device includes a plurality of flash memory blocks, the one or more programs including instructions that when executed by the one or more processors cause the storage controller to:

divide each of the plurality of flash memory devices into a plurality of logical chunks, wherein each logical chunk includes one or more flash memory blocks;

detect a predefined trigger condition with respect to a respective flash memory device of the plurality of flash memory devices;

in response to detecting the predefined trigger condition;

select one of the plurality of logical chunks of the respective flash memory device for migration in accordance with predefined selection criteria; and

store a replicated logical chunk, comprising a copy of the selected logical chunk, at a second flash memory device different from the respective flash memory device; and

remap an address of the selected logical chunk to a physical location of the replicated logical chunk; and

decrease a number of logical chunks associated with the respective flash memory device.

22. The non-transitory computer readable storage medium of claim 21, wherein the logical chunks are allocated for storing data and are organized into a plurality of redundancy sets, each redundancy set comprising one or more logical chunks and storing redundant data sufficient to enable recovery of data stored in at least one of the one or more logical chunks.

23. The non-transitory computer readable storage medium of claim 22, wherein the replicated logical chunk is included in a respective redundancy set of the plurality of redundancy sets that formerly included the selected logical chunk.

24. The non-transitory computer readable storage medium of claim 22, wherein a respective redundancy set of the plurality of redundancy sets is a contiguous stripe across the plurality of flash memory devices, and wherein the replicated logical chunk is stored in a same contiguous stripe as the selected logical chunk at the second flash memory device different from the respective flash memory device.

25. The non-transitory computer readable storage medium of claim 22, wherein the replicated logical chunk is stored in accordance with a preferred storage utilization scheme, the method including, associating the replicated logical chunk with a respective redundancy set of the plurality of redundancy sets in an indirection table.