Apparatus, system, and method for graceful cache device degradation

• US 8,443,134 B2
• Filed: 09/17/2010
• Issued: 05/14/2013
• Est. Priority Date: 12/06/2006
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: Fusion-IO Incorporated (Western Digital Corporation)
• Inventors: Flynn, David
• Primary Examiner(s): Gu, Shawn X
• Application Number:
  US12/885,285
• Publication Number:
  US 20110047437A1
• Time in Patent Office: 970 Days
• Field of Search: None
• US Class Current: 711/103
• CPC Class Codes: G06F 11/108 Parity data distribution in semiconductor storages, e.g. in SSD
• 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: G06F 2211/103 Hybrid, i.e. RAID systems with parity comprising a mix of RAID types
• CPC Class Codes: G06F 2212/2022 Flash memory
• CPC Class Codes: G06F 3/0616 in relation to life time, e.g. increasing Mean Time Between Failures [MTBF]
• CPC Class Codes: G06F 3/0619 in relation to data integrity, e.g. data losses, bit errors
• CPC Class Codes: G06F 3/0656 Data buffering arrangements
• CPC Class Codes: G06F 9/52 Program synchronisation; Mutual exclusion, e.g. by means of semaphores
• CPC Class Codes: H04L 12/403 with centralised control, e.g. polling
• CPC Class Codes: H04L 12/6418 Hybrid transport
• CPC Class Codes: H04L 67/1097 for distributed storage of data in networks, e.g. transport arrangements for network file system [NFS], storage area networks [SAN] or network attached storage [NAS]
• CPC Class Codes: H05K 7/1444 Complex or three-dimensional-arrangements; Stepped or dual mother boards

Abstract

Apparatuses, systems, and methods are disclosed for implementing a cache policy. A method may include determining a risk of data loss on a cache device. The cache device may comprise a non-volatile storage device configured to perform cache functions for a backing store. The cache device may implement a cache policy. A method may include determining that a risk of data loss on the cache devices exceeds a threshold risk level. A method may include implementing a modified cache policy for the cache device in response to the risk of data loss exceeding the threshold risk level. The modified cache policy may reduce the risk of data loss below the threshold level.

Claims

1. A method for caching using a nonvolatile storage device, the method comprising:

determining a risk of data loss on a cache device, wherein the cache device is a non-volatile storage device configured to perform cache functions for a backing store and implements a cache policy;

determining that the risk of data loss on the cache device exceeds a threshold risk level; and

implementing a modified cache policy for the cache device in response to the risk of data loss exceeding the threshold risk level, the modified cache policy reducing the risk of data loss below the threshold risk level.

2. The method of claim 1, wherein the cache policy specifies how the cache device responds to one or more of read requests and write requests.

3. The method of claim 1, wherein determining the risk of data loss comprises gauging a physical health of the cache device, and wherein the risk of data loss increases as the physical health of the cache device degrades.

4. The method of claim 1, further comprising identifying a plurality of cache policies that reduce the risk of data loss below the threshold risk level, and selecting a modified cache policy that provides a highest level of cache functionality from the plurality of cache policies.

5. The method of claim 1, wherein implementing the modified cache policy for the cache device comprises dynamically implementing the modified cache policy that reduces the risk of data loss below the threshold risk level.

6. The method of claim 5, wherein the modified cache policy reduces the risk of data loss by ensuring that data associated with write requests is preserved on the backing store.

7. The method of claim 1, wherein the modified cache policy is one of:

a write through cache policy;

a write around cache policy;

a read only cache policy; and

a bypass cache policy.

8. The method of claim 1, wherein the cache device is a solid state storage device having a plurality of banks of solid-state storage elements, wherein the cache device sequences execution of solid-state storage commands such that a first command of a first execution duration executes on a first bank concurrently with execution of a second command of a second execution duration on a second bank.

9. The method of claim 8, wherein the cache device generates an error-correcting code (ECC) chunk comprising at least a portion of received data and an ECC code capable of correcting an error in the ECC chunk, and wherein the cache device further stores a first portion of the ECC chunk on a first solid-state storage element and a second portion of the ECC chunk on a second solid-state storage element.

10. The method of claim 1, wherein the cache device comprises a plurality of physical devices cooperating such that the plurality of physical devices serve as a single logical cache device.

11. The method of claim 1, further comprising:

determining a cache device state of the cache device; and

determining the risk of data loss for the cache device in response to the cache device state.

12. An apparatus for caching using a nonvolatile storage device, the apparatus comprising:

a direct cache configured for communication with a cache device and a backing store, wherein the cache device is a non-volatile storage device configured to perform cache functions for the backing store, the direct cache comprising;

a monitor module configured for determining a risk of data loss on

the cache device;

a cache policy module configured for implementing a modified cache policy for the cache device if a risk of data loss on the cache device exceeds a threshold risk level; and

wherein the direct cache is configured to recieve, from the cache device,

one or more indicators associated with the risk of data loss on the cache device.

13. The apparatus of claim 12, wherein the cache policy module is further configured to send write requests to the cache device, send the write requests to the backing store, and receive acknowledgements in response to the backing store fulfilling the write requests.

14. The apparatus of claim 12, wherein the cache policy module is further configured to send write requests exclusively to the backing store such that the write requests bypass the cache device and to receive acknowledgements in response to the backing store fulfilling the write requests.

15. The apparatus of claim 14, wherein the cache policy module is further configured to first direct read requests to the cache device for fulfillment.

16. The apparatus of claim 12, wherein the cache policy module is further configured to bypass the cache device such that write requests are sent exclusively to the backing store, and such that read requests are sent exclusively to the backing store.

17. The apparatus of claim 12, wherein the direct cache communicates with the cache device using a caching interface.

18. The apparatus of claim 12, wherein the direct cache is a stand-alone driver.

19. A system for caching using a nonvolatile storage device, the system comprising:

a backing store configured for storing data received from one or more storage clients,

wherein the backing store comprises one or more non-volatile storage devices;

a cache device configured for performing cache functions for the backing store,

wherein the cache device is a non-volatile storage device with faster access characteristics than those of the backing store, and wherein the cache device is configured to implement a cache policy;

a direct cache configured for;

determining a risk of data loss on the cache device;

determining that the risk of data loss on the cache device exceeds a threshold risk level; and

implementing a modified cache policy for the cache device in response to the risk of data loss exceeding the threshold risk level, the modified cache policy reducing the risk of data loss below the threshold risk level.

20. The system of claim 19, wherein the direct cache is configured to communicate with the cache device using a caching interface.

21. The system of claim 19, wherein the cache policy specifies how the cache device responds to one or more of read requests and write requests received from the one or more storage clients.

22. The system of claim 19, wherein the modified cache policy reduces the risk of data loss by ensuring that data associated with write requests is preserved on the backing store.