Patent ID: 8615628

Claim:
A storage system coupled to a client comprising: a storage device having a plurality of disk drives each of which included in one of a plurality of RAID groups; and a controller configured to: control an access request to a plurality of files stored in the storage device; manage access time of each file; memorize the access time of each file upon receiving an access request to the file; classify the plurality of files into a plurality of groups according to the access time of each file, each of the plurality of groups corresponding to the RAID groups; relate each of the plurality of groups to the corresponding RAID group for which a predetermined time period for spinning down disk drives of the RAID group does not include an access time period of the RAID group; migrate a first file of the plurality of files so that files classified into a first group of the plurality of groups are stored in a first RAID group of the plurality of RAID groups; and spin down the disk drives of the first RAID group in a predetermined time period of the first RAID group, and wherein the access time period of the first RAID group is calculated based on the access time of the files included in the first group and a required time to spin up and spin down the disk drives.