Dynamic storage allocation system for a prioritized cache

Abstract

Methods for managing a Least Recently Used (LRU) cache in a staged storage system on a prioritized basis permitting management of data using multiple cache priorities assigned at the data set level. One method uses the signed difference between an assigned and actual hit ratio to dynamically allocate cache size to a class of data and its correlation with priority of that class. Advantageously, the hit ratio performance of a class of data can not be degraded beyond a predetermined level by a class of data having lower priority. Another method dynamically reallocates cache space among partitions asymptotically to the general equality of a weighted hit rate slope function attributable to each partition. This function is the product of the slope of a weighting factor and the partition hit rate versus partition space allocation function. Cache space is dynamically reallocated among the partitions in a direction that forces the weighted hit rate slope for each partition into equality over the entire cache. Partition space is left substantially unchanged in those partitions where the weighted hit rate slope is non-positive. Hit rate is defined as hit ratio times I/O rate.