US Patent 7130961 Disk controller and method of controlling the cache

To execute cache data identity control between disk controllers in plural disk controllers provided with each cache. To prevent a trouble from being propagated to another disk controller even if the trouble occurs in a specific disk controller. The identity control of data is executed via a communication means between disk controllers. In case update access from a host is received, data in a cache memory of a disk controller that controls at least a data storage drive is updated. It is desirable that a cache area is divided into an area for a drive controlled by the disk controller and an area for a drive controlled by another disk controller and is used.