Cache management using favored volumes and a multiple tiered cache memory

A method for demoting selected storage elements within a storage system, the storage system including at least one processor, a cache memory, and a computer-readable storage medium having computer-usable program code embodied therein, the computer-usable program code configured to perform the method when executed by the at least one processor, the method comprising:

• storing favored storage elements and non-favored storage elements within the cache memory, the cache memory comprising a higher performance portion and a lower performance portion;
• maintaining a first favored LRU list and a first non-favored LRU list within the higher performance portion, wherein the first favored LRU list includes entries associated with the favored storage elements stored within the higher performance portion and ordered according to when the favored storage element was recently accessed, and wherein the first non-favored LRU list includes entries associated with the non-favored storage elements stored within the higher performance portion and ordered according to when the non-favored storage element was recently accessed;
• selecting a first selected storage element from the first favored LRU list or the first non-favored LRU list to demote from the higher performance portion when space is needed in the higher performance portion, wherein the selecting the first selected storage element comprises selecting an oldest favored storage element from the first favored LRU list if the first non-favored LRU list is empty and selecting an oldest non-favored storage element from the first non-favored LRU list if the first favored LRU list is empty;
• and
• demoting the first selected storage element from the cache memory, or from the higher performance portion to the lower performance portion, according to a cache demotion policy.

A storage controller for demoting selected storage elements within a storage system, the storage controller including a processor, a cache memory, and a non-transitory computer-readable storage medium having computer-usable program code embodied therein, the computer-usable program code configured to perform operations when executed by the processor, the operations comprising:

• storing favored storage elements and non-favored storage elements within the cache memory, the cache memory comprising a higher performance portion and a lower performance portion;
• maintaining a first favored LRU list and a first non-favored LRU list within the higher performance portion, wherein the first favored LRU list includes entries associated with the favored storage elements stored within the higher performance portion and ordered according to when the favored storage element was recently accessed, and wherein the first non-favored LRU list includes entries associated with the non-favored storage elements stored within the higher performance portion and ordered according to when the non-favored storage element was recently accessed;
• selecting a first selected storage element from the first favored LRU list or the first non-favored LRU list to demote from the higher performance portion when space is needed in the higher performance portion, wherein the selecting the first selected storage element comprises selecting an oldest favored storage element from the first favored LRU list if the first non-favored LRU list is empty and selecting an oldest non-favored storage element from the first non-favored LRU list if the first favored LRU list is empty;
• and
• demoting the first selected storage element from the cache memory, or from the higher performance portion to the lower performance portion, according to a cache demotion policy.