Patent ID: 8918620

Claim:
A storage system comprising: a plurality of RAID groups each including a plurality of storage devices; a controller configured to associate a plurality of logical volumes with each of the RAID groups, and to allot at least one of the plurality of logical volumes to a virtual volume; and a memory configured to store a piece of access conversion information for converting access to the virtual volume into access to the allotted logical volume, wherein the controller is configured to: convert the access to the logical volume into the access to the associated RAID group in response to the access to the corresponding virtual volume on the basis of the access conversion information, monitor frequency of access to each of the logical volumes, select a logical volume on the basis of the monitored frequency of access, move data stored in a RAID group corresponding to the selected logical volume to a different RAID group corresponding to a logical volume to be a data shift destination, and update the access conversion information to convert access to the RAID group corresponding to the selected logical volume into access to the different RAID group.