Patent ID: 8495288

Claim:
A storage system comprising: a first storage controller including: a first communications controller for carrying out data communications with a host computer; a second communications controller for carrying out data communications with a storage device; a cache memory that is used in the exchange of data between the first communications controller and the second communications controller, wherein said cache memory is used for both write and read operations; a controller for controlling the first communications controller, the second communications controller and the cache memory respectively; a determination data setting unit for setting, in respective data, and determination data for making a primary determination as to whether or not the respective data matches with other data; a second storage controller including: a duplicated data detector, which is for detecting whether or not a plurality of prescribed data is duplicated data, and which comprises a primary determination unit that makes a primary determination as to whether or not the respective prescribed data match with one another by comparing the respective determination data set in the respective prescribed data, and a secondary determination unit that compares the respective prescribed data and makes a secondary determination as to whether or not the respective prescribed data is duplicated data when the primary determination unit makes a primary determination that the respective prescribed data match with one another; and a duplicated data processor that implements a preconfigured prescribed process for the duplicated data, when a secondary determination is that the respective prescribed data is duplicated data, wherein at least the determination data setting unit and the secondary determination unit are configured as dedicated circuits that are separate from the controller, wherein said determination data setting unit provides a hash value of write data received from said host computer to said cache memory, wherein the first controller stores the write data received from said host computer with the hash value of the write data to the storage device, and the second storage controller receives the write data received from said host computer with the hash value of the write data, and wherein the duplicated data processor stores only one data of the duplicated data to a differential backup volume coupled to the second storage controller, and deletes the other data of the duplicated data.