Exclusive caching in computer systems
View Patent ↗A computer system with mechanisms for exclusive caching that avoids the accumulation of duplicate copies of information in host and storage system caches. A computer system according to these exclusive caching techniques includes a host system having a host cache and a storage system having a storage system cache and functionality for performing demote operations to coordinate the placement of information in the host cache to the storage system caches.
1. A method for exclusive caching between a storage system cache of a storage system and a host cache of a host system, comprising the steps of:
providing the host system with access to the information by reading the information from the storage system cache and then storing the information in the host cache and evicting the information from the storage system cache such that the information does not occupy space in both the host and storage system caches;
demoting the information from the host cache to the storage system cache if the information is clean when evicted from the host cache such that the information does not occupy space in both the host and storage system caches.
2. The method of claim 1 , wherein the step of demoting comprises the step of transferring the information to the storage system cache in a demoted data block.
3. The method of claim 1 , wherein the step of demoting comprises the step of storing the information in any free area of the storage system cache.
4. The method of claim 1 , wherein the step of demoting cache comprises the step of storing the information in a predetermined sub-area of the storage system cache.
5. The method of claim 1 , wherein the step of demoting includes the step of evicting a data block from the storage system cache.
6. The method of claim 5 , wherein the step of evicting includes the step of selecting the data block for eviction from the storage system cache from among a set of unshared data blocks in the storage system cache.
7. The method of claim 5 , wherein the step of evicting includes the step of selecting the data block for eviction from the storage system cache using a shared status of the data block as a factor in a replacement policy.
8. A computer system, comprising:
storage system having a storage media and a storage system cache;
host system having a host cache;
means for exclusively caching a set of information obtained from the storage media such that the information is stored either in the host cache or the storage system cache but not both caches at the same time wherein the means for exclusively caching includes means for reading the information from the storage system cache and then storing the information in the host cache and evicting the information from the storage system cache and means for demoting the information from the host cache to the storage system cache if the information is clean when evicted from the host cache.
9. The computer system of claim 8 , wherein the means for demoting comprises means for transferring the information to the storage system cache in a demoted data block via a communication path between the host system and the storage system.
10. The computer system of claim 8 , wherein the means for demoting comprises means for storing the information in any free area of the storage system cache.
11. The computer system of claim 8 , wherein the means for demoting comprises means for storing the information in a predetermined sub-area of the storage system cache.
12. The computer system of claim 8 , wherein the means for demoting includes means for evicting a data block from the storage system cache.
13. The computer system of claim 12 , wherein the means for evicting includes means for selecting the data block for eviction from the storage system cache from among a set of unshared data blocks in the storage system cache.
14. The computer system of claim 12 , wherein the means for evicting means for selecting a data block for eviction from the storage system cache using a shared status of the data block as a factor in a replacement policy.
15. The computer system of claim 8 , wherein the storage system cache includes a sub-area for exclusive caching and a sub-area holding other cached information.
16. The computer system of claim 15 , wherein the other cached information is obtained by performing read-ahead operations from the storage media.
17. The computer system of claim 8 , further comprising means for transferring the information evicted from the host cache to the storage system in a write operation if the information is dirty.
18. The computer system of claim 8 , wherein the host cache is a RAM cache.
19. The computer system of claim 8 , wherein the host cache is a disk cache.