In a storage system in which: LSW 110 is a local switch, GSW 115 is a global switch, and 21 is a global shared memory unit; when a host computer 3 makes a data read request to a disk control cluster 1-1, a channel interface unit 11 accesses to a local shared memory unit 22 via the LSW 110, and if the data exists in the disk control cluster 1-1, the channel interface unit 11 read the data from the local shared memory unit 22 or the disk drive 2 so as to transfer to the host computer 3. If the data is not in the disk control cluster 1-1, the channel interface unit 11 accesses to the global shared memory unit 21, check a disk control cluster with the requested data stored therein, obtains the requested data from the disk control cluster where the requested data is stored, and transfer the data to the host computer 3. This provides a storage system with a configuration of a desirable scalability and with architecture for high reliability and high performance of the disk control clusters that can deal with a wide range of configurations from a small-scale configuration to a super huge configuration