Patent ID: 6877065

Claim:
A method of caching data for a direct access storage device (DASD) having a plurality of addressable locations, comprising the steps of: storing, in a DASD cache memory having a total usable hardware memory capacity for a DASD cache, copies of data retrieved from said direct access storage device, and a cache directory identifying data in said direct access storage device for which copies are stored in said cache memory, and identifying memory locations in said cache memory where each said copy is stored, responding to a request for access to a DASD storage device location for which a copy is stored in the cache memory, by accessing the copy stored in the cache memory, responding to a request for access to a desired DASD storage device location for which a copy is not stored in the cache memory, by accessing said desired storage device location from said storage device, and responding to a change in said total usable hardware cache memory capacity for said DASD cache by altering said cache directory.