Patent ID: 8239626

Claim:
A storage system, comprising: a plurality of flash memory devices; and a controller configuring a plurality of logical volumes formed based on a storage area group that constitutes the storage space of the plurality of flash memory devices, wherein the controller performs access, based on a RAID level corresponding to the logical volume, to each of the storage areas of each of two or more flash memory devices that constitute an access destination logical volume, wherein the controller calculates the load of each of the flash memory devices based on a load that accompanies the access to each storage area, wherein the controller executes load distribution processing to distribute the loads of the plurality of flash memory devices, wherein, in the load distribution processing, the controller selects one storage area from two or more storage areas of a high load flash memory device, selects a flash memory device with a lower load than that of the flash memory device, and makes a determination of whether the redundancy according to the RAID level decreases when data elements stored in the selected storage area are transferred to the selected low load flash memory device, wherein when a result of the determination is that the redundancy does not decrease, the controller transfers the data elements stored in the selected storage area to a buffer area of the selected low load flash memory device, which is a storage area used as a buffer that does not correspond to a logical address space of the logical volume, and associates the logical address space of the logical volume that corresponds to the selected storage area with the buffer area, and wherein when a result of the determination is that the redundancy decreases, the controller selects a flash memory device which has a lower load than the load of the high load flash memory device, and has a higher load than the flash memory device selected in the previous determination.