Patent ID: 7774550

Claim:
A storage system comprising: a storage apparatus comprising at least one or more rewritable storage devices for storing data expected to be read out sequentially; a cache memory for storing the data to be read out from the storage apparatus; a prefetch section for reading out, in advance, the data stored in the storage apparatus and storing the data in the cache memory before a sequential read access is received from a host; a continuity determination section for determining a continuity measure indicative of the continuity of the arrangement of the data stored in the storage apparatus which is calculated from a cache hit rate of read accesses issued from the host when the prefetch section is ON, wherein the cache hit rate was determined with the assumption that the prefetch section was ON when in fact the prefetch section was OFF; a prefetch quantity calculator for calculating a prefetch quantity on the basis of the continuity measure and the state of a read access from the host; and a prefetch operation controller for setting the prefetch quantity calculated by the prefetch quantity calculator in the prefetch section, and controlling the operation of the prefetch section based on the continuity measure, wherein when the prefetch section is ON then the continuity measure is computed as FI=Ch−b/ 1 −b where FI is the continuity measure, Ch is the cache hit rate, and b is a constant (0<b<1).