A storage system is arranged to speed up the operation and easily duplicate data without the capacity of the cache memory being so large even if lots of host computers are connected with the storage system. This storage system includes channel adapters, disk drives, disk adapters, and network switches. Further, the front side cache memories connected with the channel adapters and the back side cache memories connected with the disk adapters are provided as two layered cache system. When a request for writing data is given to the storage system by the host computer, the data is written in both the front side cache memory and the back side cache memory. The write data is duplicated by placing the write data in one of the front side cache memories and one of the back side cache memories or two of the back side cache memories.
