CACHING METHOD FOR DATA BLOCKS OF VARIABLE SIZE

摘要

A caching method (30) for selecting variable size data blocks for removal from a cache (14) for a virtual tape subsystem (10) or other cached system of computer data storage includes determining (32, 34) the size and the unreferenced time interval of each data block in the cache. The size of a data block is the amount of cache space taken up by the block. The unreferenced time interval of a data block is the time that has elapsed since the block was last accessed. The recall probability per unit time of each data block in the cache is then determined (38). The recall probability of a data block is a function of its unreferenced time interval and possibly size and other auxiliary parameters. The caching method then determines (40) a quality factor (q) for each data block. The quality factor (q) of a data block is a function of its recall probability and size. The caching method concludes with removing (42) from the cache the data block with the lowest quality factor (q).