Patent ID: 8261036

Claim:
A storage system coupled to an external storage system and a host computer, the storage system comprising: a plurality of storage devices configuring a plurality of RAID groups, one or more logical volumes being configured on storage spaces provided by each of the RAID groups; a shared memory for storing configuration information on the logical volumes being configured on the RAID groups and logical storage being configured on storage spaces provided by the external storage system, the information indicating which storage spaces of the RAID groups or the external storage system each of logical volumes being configured on; and one or more processors for processing I/O requests from the host computer addressed to the logical volumes on the RAID groups and the external storage system, wherein the one or more processors are configured to execute migrating all data in the logical volumes on the external storage system within storage spaces provided by one of the RAID groups, updating the configuration information on the logical volumes on the external storage system, and shifting a state of the external storage system to a power-saving state.