Applying storage device commit-cached-data-to-media functionality to improve data security in systems that allow storage devices to cache writes

• US 20060020752A1
• Filed: 07/20/2005
• Published: 01/26/2006
• Est. Priority Date: 07/21/2004
• Status: Active Grant

• Current Assignee: Infortrend Technology Incorporated (Infortrend Corporation)
• Original Assignee: Infortrend Technology Incorporated (Infortrend Corporation)
• Inventors: Schnapp, Michael Gordon, Hung, Ching-Hai
• Granted Patent: US 8,019,937 B2
• Time in Patent Office: Days
• US Class Current: 711/113
• CPC Class Codes: G06F 12/0804 with main memory updating G06F12/0806 takes precedence
• CPC Class Codes: G06F 12/0811 with multilevel cache hierarchies
• CPC Class Codes: G06F 12/0866 for peripheral storage systems, e.g. disk cache
• CPC Class Codes: G06F 2212/1032 Reliability improvement, data loss prevention, degraded operation etc

Abstract

A method for committing cached data to storage media including a host entity and a physical storage device (PSD), comprising: the host entity issuing a write IO request to the PSD being in write-back caching mode to write data from a host memory to the PSD; the host entity receiving a successful IO completion response associated with the write IO request from the PSD and recording an entry of the write IO request to a selected list; the host entity issuing a synchronized cache IO request to the PSD; the PSD responding a successful IO completion response of the synchronized cache IO request to the host entity; the host entity extracting the entry of the write IO request from the selected list before issuing the synchronized cache IO request; and the host entity engaging completion processing of write IO request corresponding to the entry of the write IO request extracted.

Claims

1. A method for committing cached data to storage media in a storage system including a host entity and a physical storage device (PSD), the PSD comprising the storage media and a cache memory for containing the cached data, the method comprising the steps of:

the host entity issuing a write IO request to the PSD being in write-back caching mode to write associated data from a host memory to the PSD;

the host entity receiving a successful IO completion response associated with the write IO request from the PSD and recording an entry of the write IO request to a selected list;

the host entity issuing a synchronized cache IO request to the PSD to have the PSD commit cached data to the storage media;

the PSD responding a successful IO completion response of the synchronized cache IO request to the host entity;

when the host entity receives the synchronized cache IO request completion response from the PSD, the host entity extracting the entry of the write IO request from the selected list before issuing the synchronized cache IO request; and

the host entity engaging completion processing of write IO request corresponding to the entry of the write IO request extracted.

2. The method of claim 1, wherein when the host entity receives the IO completion response of the synchronized cache IO request from the PSD, the host entity extracts the entry of the write IO request from the selected list before receiving the synchronized cache IO request completion response.

3. The method of claim 1, further comprising the steps of:

the host entity queuing up any new write IO requests to write data from the host memory to the PSD pending completion of the synchronized cache IO request and waiting for completion of all write IO requests currently in the process of execution before the step of issuing the synchronized cache IO request to the PSD; and

the host entity de-queuing the queued IO requests for execution after the host entity receiving the synchronized cache IO request completion response.

4. The method of claim 1, further comprising the step of the host entity selecting an alternate list as the selected list for receiving successful IO completion response after the step of issuing the synchronized cache IO request to the PSD.

5. The method of claim 1, further comprising the step of issuing a second synchronized cache IO request to the PSD before a first synchronized cache IO request completion response is received.

6. The method of claim 1, further comprising the step of, when the host entity receives an operation failed IO completion response of the synchronized cache IO request from the PSD, the host entity reissues a synchronized cache IO request to the PSD.

7. The method of claim 6, further comprising the step of, the host entity reissuing the write IO requests in the selected list before the host entity reissues the synchronized cache IO request to the PSD.

8. The method of claim 6, further comprising the step of determining whether the reissued synchronize cache operation succeeds, if the synchronized cache operation fails again, a recovery procedures is engaged.

9. The method of claim 6, further comprising the step of determining whether the reissued synchronize cache operation succeeds, if the synchronized cache operation fails again, the retried write IO requests is posted as having failed.

10. The method of claim 6, further comprising the step of determining whether the reissued synchronize cache operation succeeds, if the synchronized cache operation fails again, the host entity retries to reissue the synchronized cache IO request to the PSD.

11. The method of claim 10, further comprising the step of determining whether a maximum retry count is reached.

12. The method of claim 1, wherein when the host entity receives an operation failed IO completion response of the synchronized cache IO request from the PSD, the host entity requests the PSD to operate in write-through caching mode.

13. The method of claim 12, further comprising the step of, the host entity reissuing the write IO requests in the selected list after requesting the PSD to operate in write-through caching mode.

14. The method of claim 1, wherein when the host entity receives an operation failed IO completion response of the synchronized cache IO request from the PSD, the host entity reissues the write IO requests in the selected list by the following steps of:

(a) the host entity issuing the write IO request in the selected list;

(b) the host entity issuing a synchronized cache IO request after receiving a IO completion response of the write IO request;

(c) the host entity extracting the entry of the write IO request from the selected list after receiving a IO completion response of the synchronized cache IO request; and

repeating the steps (a) through (c) until the selected list is empty.

15. The method of claim 14, further comprising the step of, if the IO completion response of the synchronize cache IO request indicates failure of the synchronize cache IO request, the retried write IO request is posted as having failed

16. The method of claim 1, wherein when the host entity receives an operation failed IO completion response of the synchronized cache IO request from the PSD, the host entity extracting the entry of the write IO request from the selected list and reissuing each one with each write IO request individually requesting the PSD use write-through caching to process the request.

17. The method of claim 1, wherein when the host entity receives an operation failed IO completion response of a synchronized cache IO request from the PSD, the PSD is switched to write-through caching mode on a per-write-IO-request-retry basis.

18. The method of claim 17, further comprising the steps of, (a) the PSD being switched to write-through caching mode;

(b) the host entity issuing a write IO request in the selected list;

(c) the PSD being switched back to write-back caching mode and the host entity extracting the entry of the write IO request from the selected list after the host entity receives a IO completion response of the write IO request; and

repeating the steps (a) through (c) until the selected list is empty.

19. The method of claim 1, wherein when the host entity receives an operation failed IO completion response of a synchronized cache IO request from the PSD, the PSD is switched to write-through caching mode entirely for the entire course of an error recovery process.

20. The method of claim 19, further comprising the steps of,

(a) the PSD being switched to write-through caching mode;

(b) the host entity issuing write IO requests in the selected list;

(c) the host entity extracting the entry of the write IO requests from the selected list after the host entity receives a IO completion response of the write IO requests;

(d) the host entity repeating the steps (b) through (c) until the selected list is empty; and

(e) the PSD being switched back to write-back caching mode.

21. The method of claim 1, wherein when the host entity receives an operation failed IO completion response of a synchronized cache IO request from the PSD, the host entity determines whether the PSD supports write-through write cache policy and determines whether the PSD support the specification of write-cache policy on a per IO basis, the host entity performs a recovery process in accordance with the determinations.

22. The method of claim 1, further comprising a timing determining step to determine a timing for issuing the synchronized cache IO request to the PSD before the step of issuing a synchronized cache IO request.

23. The method of claim 22, wherein the timing determining step comprises the steps of defining criteria for issuing the synchronized cache IO request, and determining the timing reached when the criteria is met.

24. The method of claim 23, wherein the criteria for issuing the synchronized cache IO request is that the number of entries on the selected list exceeds a first threshold.

25. The method of claim 23, wherein the criteria for issuing the synchronized cache IO request is that total amount of data associated with entries on the selected list exceeds a second threshold.

26. The method of claim 23, wherein the criteria for issuing the synchronized cache IO request is that the time transpired since the first write IO request was entered into the selected list exceeds a third threshold.

27. The method of claim 23, wherein the criteria for issuing the synchronized cache IO request is that there is a write IO request to be issued by the host entity for the time being.

28. The method of claim 23, wherein the criteria for issuing the synchronized cache IO request is that one of the following conditions is satisfied:

(a) the number of entries on the selected list exceeds a first threshold;

(b) total amount of data associated with entries on the selected list exceeds a second threshold;

(c) the time that has transpired since the first write IO request was entered into the selected list exceeds a third threshold; and

(d) for the time being, there is any write IO request to be issued by the host entity.

29. The method of claim 23, wherein the criteria for issuing the synchronized cache IO request is that one of the following conditions is satisfied:

(a) the time that has transpired since the first write IO request was entered into the selected list exceeds a third threshold; and

(b) there is any write IO request to be issued by the host entity for the time being.

30. The method of claim 23, wherein the criteria for issuing the synchronized cache IO request can be dynamically adjusted.

31. The method of claim 23, wherein the criteria for issuing the synchronized cache IO request can be automatically adjusted according to storage system states.

32. The method of claim 31, wherein the criteria is automatically adjusted in response to variation of data buffering resources of the storage system.

33. A storage system including a host entity and a physical storage device (PSD) to write data from the host entity to the PSD, the PSD comprising storage media and a cache memory for containing cached data, the storage system comprising a PSD mechanism for committing cached data to the storage media and performing the following steps:

the host entity issuing a write IO request to the PSD being in write-back caching mode to write associated data from a host memory to the PSD;

the host entity receiving a successful IO completion response associated with the write IO request from the PSD and recording an entry of the write IO request to a selected list;

the host entity issuing a synchronized cache IO request to the PSD;

the PSD responding a successful IO completion response of the synchronized cache IO request to the host entity;

when the host entity receives the successful IO completion response of the synchronized cache IO request from the PSD, the host entity extracting the entry of the write IO request from the selected list before issuing the synchronized cache IO request; and

the host entity engaging completion processing of write IO request corresponding to the entry of the write IO request extracted.

34. A computer system comprising a storage system connected thereto, the storage system including a host entity and a physical storage device (PSD) to write data from the host entity to the PSD, the PSD comprising storage media and a cache memory for containing cached data, the computer system comprising a PSD mechanism for committing cached data to the storage media and performing the following steps:

the host entity issuing a write IO request to the PSD being in write-back caching mode to write associated data from a host memory to the PSD;

the host entity receiving at least one successful IO completion response associated with the write IO request from the PSD and recording an entry of the write IO request to a selected list;

the host entity issuing a synchronized cache IO request to the PSD;

the PSD responding a successful IO completion response of the synchronized cache IO request to the host entity;

when the host entity receives a successful IO completion response of the synchronized cache IO request from the PSD, the host entity extracting the entry of the write IO request from the selected list before issuing the synchronized cache IO request; and

the host entity engaging completion processing of write IO request corresponding to the entry of the write IO request extracted.