Patent ID: 7873866

Claim:
A computer system comprising: a plurality of storage systems accessed by a host computer, the plurality of storage systems including a first storage system and a second storage system, the first storage system including at least one first interface coupled to the host computer and the second storage system, a first processor coupled to the first interface, a first memory coupled to the first processor and a plurality of first storage devices for storing data read and written by the host computer, the second storage system including at least one second interface coupled to the host computer and the first storage system, a second processor coupled to the second interface, a second memory coupled to the second processor and a plurality of second storage devices for storing data read and written by the host computer, wherein the first storage system determines whether or not the number of the first storage devices under normal operation in the first storage system is larger than a predetermined threshold, determines whether or not data stored in the first storage devices under normal operation can be migrated to the second storage devices if the number of the first storage devices under normal operation is equal to or smaller than the predetermined threshold, duplicates the data stored in the first storage devices under normal operation to the second storage devices if the data stored in the first storage devices under normal operation can be migrated to the second storage devices, and outputs information indicating that the first storage system can be removed from the computer system.