Method for Selectively Enabling and Disabling Read Caching in a Storage Subsystem

• US 20090037662A1
• Filed: 07/30/2007
• Published: 02/05/2009
• Est. Priority Date: 07/30/2007
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Martin, Joshua Douglas, Thompson, James Russell, Miller, Justin Thomas, Miller, Vernon Walter, Xu, Yan, La Frese, Lee Charles, Yiparaki, Olga
• Granted Patent: US 8,874,854 B2
• Time in Patent Office: Days
• US Class Current: 711/136
• CPC Class Codes: G06F 12/0888 using selective caching, e.g. bypass

Abstract

A mechanism for selectively disabling and enabling read caching based on past performance of the cache and current read/write requests. The system improves overall performance by using an autonomic algorithm to disable read caching for regions of backend disk storage (i.e., the backstore) that have had historically low cache hit ratios. The result is that more cache becomes available for workloads with larger hit ratios, and less time and machine cycles are spent searching the cache for data that is unlikely to be there.

Claims

1. A computer-implementable method for disabling and enabling read caching based on past performance of a cache requests comprising:

performing a selective read caching function, the selective read caching function selectively enabling and disabling read caching for individual regions of a backstore depending on whether read caching has provided any recent benefit.

2. The computer implementable method of claim 1, wherein the selective read caching function further comprises:

dividing the backstore into a plurality of logical backstore units (LBUs); and

,

selectively enabling and disabling read caching for each of the plurality of LBUs.

3. The computer implementable method of claim 2, wherein:

a read hit ratio is recorded for each of the plurality of LBUs while a read cache is enabled; and

,

when the read hit ratio of an LBU is below a predefined threshold, the read cache is disabled for the LBU.

4. The computer implementable method of claim 3, wherein:

while the read cache is disabled, the distribution of read accesses to the LBU is recorded over short time intervals; and

,

read caching is enabled when one portion of the LBU has significantly more read accesses than other LBUs.

5. The computer implementable method of claim 4, wherein:

the short time intervals correspond to a cache residency time value.

6. The computer implementable method of claim 3, wherein:

read caching is enabled automatically over a longer time interval, regardless of read access distribution.

7. The computer implementable method of claim 3, wherein:

when read caching is disabled for an LBU, determining that a read request cannot be satisfied from the write cache, without searching the write cache.

8. A system comprising:

a processor;

a cache coupled to the processor;

a backstore coupled to the cache and the processor; and

a computer-usable medium embodying computer program code, the computer program code comprising instructions executable by the processor and configured for;

performing a selective read caching function, the selective read caching function selectively enabling and disabling read caching for individual regions of the backstore depending on whether read caching has provided any recent benefit.

9. The system of claim 8, wherein the computer program code further comprises instructions executable by the processor and configured for:

dividing the backstore into a plurality of logical backstore units (LBUs); and

,

selectively enabling and disabling read caching for each of the plurality of LBUs.

10. The system of claim 9, wherein:

a read hit ratio is recorded for each of the plurality of LBUs while a read cache is enabled; and

,

when the read hit ratio of an LBU is below a predefined threshold, the read cache is disabled for the LBU.

11. The system of claim 10, wherein:

while the read cache is disabled, the distribution of read accesses to the LBU is recorded over short time intervals; and

,

read caching is enabled when one portion of the LBU has significantly more read accesses than other LBUs.

12. The system of claim 11, wherein:

the short time intervals correspond to a cache residency time value.

13. The system of claim 10, wherein:

read caching is enabled automatically over a longer time interval, regardless of read access distribution.

14. The system of claim 10, wherein:

when read caching is disabled for an LBU, determining that a read request cannot be satisfied from the write cache, without searching the write cache.

15. A computer-usable medium embodying computer program code, the computer program code comprising computer executable instructions configured for:

performing a selective read caching function, the selective read caching function selectively enabling and disabling read caching for individual regions of a backstore depending on whether read caching has provided any recent benefit.

16. The computer-usable medium of claim 15, wherein the computer executable instructions are further configured for:

dividing the backstore into a plurality of logical backstore units (LBUs); and

,

selectively enabling and disabling read caching for each of the plurality of LBUs.

17. The computer-usable medium of claim 16, wherein:

a read hit ratio is recorded for each of the plurality of LBUs while a read cache is enabled; and

,

when the read hit ratio of an LBU is below a predefined threshold, the read cache is disabled for the LBU.

18. The computer-usable medium of claim 17, wherein:

while the read cache is disabled, the distribution of read accesses to the LBU is recorded over short time intervals; and

,

read caching is enabled when one portion of the LBU has significantly more read accesses than other LBUs.

19. The computer-usable medium of claim 18, wherein:

the short time intervals correspond to a cache residency time value.

20. The computer-usable medium of claim 17, wherein:

read caching is enabled automatically over a longer time interval, regardless of read access distribution.

21. The computer-usable medium of claim 17, wherein:

when read caching is disabled for an LBU, determining that a read request cannot be satisfied from the write cache, without searching the write cache.