Patent ID: 8898383

Claim:
A storage system comprising: a plurality of physical memory devices storing data of a plurality of logical devices configuring RAID (Redundant Arrays of Inexpensive Disks); and a storage controller coupled to the plurality of physical memory devices, wherein each of the plurality of logical devices is a target device of an access from a data processing unit coupled to the storage system, and at least two of the plurality of physical memory devices differ in performance, wherein the storage controller is configured to reallocate data having a high access frequency to one of the plurality of physical memory devices having a better performance than the physical memory device in which the data to be reallocated is currently stored, and wherein a size of a data unit to be reallocated by the storage controller is set based on a least common multiple of an amount of data corresponding to a check information of the RAID configuration of both logical devices between which the data is to be reallocated and is larger than a data unit to be accessed from the data processing unit.