Patent ID: 7865665

Claim:
A storage system adapted to be coupled to an information processing apparatus, comprising: a controller having a first cache memory; a plurality of disk drives coupled to the controller, each of the plurality of disk drives having a second cache memory and a storage medium, the second cache memory being used for informing the controller of completion of writing after writing data in the second cache memory, so that each of the plurality of disk drives can improve write performance to the controller, wherein upon receiving a first data write request from the information processing apparatus, the controller temporarily stores first data corresponding to the data write request in the first cache memory and sends an instruction to write the first data to at least one of the plurality of disk drives, wherein upon receiving the instruction to write the first data from the controller, the at least one of the plurality of disk drives writes the first data to the second cache memory in the at least one of the plurality of disk drives and informs the controller of a completion of the writing, wherein the controller determines if a number of instructions to write data to the at least one of the plurality of disk drives exceeds a predetermined number and, if so, instructs the at least one of the plurality of disk drives to write data, including the first data, stored in the second cache memory of the at least one of the plurality of disk drives into the storage medium of the at least one of the plurality of disk drives, and wherein after writing the data, including the first data, to the storage medium, the controller determines if data stored in the first cache memory coincides with data stored in the storage medium of the at least one of the plurality of disk drives.