| 摘要 |
A method and apparatus for improving caching for a virtual tape server is disclosed. The method and apparatus improve caching by making assumptions to increase cache hits, but which do not cause the virtual tape server to under-perform when these assumptions prove to be incorrect. The method includes the steps of correlating logical volume usage to externally determined file characteristics to derive usage histories for cached logical volumes, maintaining a record of the histories for the files that share the same predefined characteristics, and managing the migration of the logical volumes according to the usage history and the externally determined file characteristics of the logical volume. The correlation is accomplished by associating the first logical volume with a logical volume type based on predefined characteristics, assigning a time bin for the type of the first logical volume based on the time of last access of the first logical volume therein and based on the type assigned to the first logical volume at the time the first logical volume was last accessed and updating a usage count in the time bin for the type. Scores for each logical volume in the cache are updated by determining the age and type of each logical volume, selecting appropriate time buckets for the logical volume, calculating a usage score for the time buckets, computing time-weighted usage scores for the time buckets and identifying a final score for the logical volume. The logical volume with the lowest score is the next volume to be discarded from the cache.
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