Patent ID: 8214595

Claim:
A storage system, comprising: one or more host interfaces coupled to one or more host computers; one or more disk drives; one or more drive interfaces coupled to the disk drives; one or more cache memories for temporarily storing at least one of data read from the disk drives and data to be written to the disk drives; and one or more control processors, wherein the cache memories comprise one or more volatile first memories, and one or more non-volatile second memories, the non-volatile second memories having a capacity larger than a capacity of the volatile second memories, wherein the volatile first memories, and the non-volatile second memories each comprise a plurality of memory areas, wherein each of the plurality of memory areas of the volatile first memories and the plurality of memory areas of the non-volatile second memories belongs either to the first kind of memory area which is associated with the data blocks of the disk drives, or to the second kind of memory area which is not associated with the data blocks of the disk drives, wherein the control processors control write and read of data to and from the volatile first memories and the non-volatile second memories, and wherein the control processors are configured to: receive requests for writing data to the disk drives or for reading data from the disk drives; store the requested data in the volatile first memories; select, if a total capacity of the second kind of memory area included in the volatile first memories is less than a predetermined threshold, one of a plurality of the first kind of memory areas of the volatile first memories; write data stored in the selected first kind of memory area of the volatile first memories in the non-volatile second memories; and change the selected first kind of memory area of the volatile first memories to the second kind of memory area of the volatile first memories.