Patent ID: 7953939

Claim:
A storage system having a plurality of disk drives and a disk controller for controlling the plurality of disk drives, with a logical device being allocated to a plurality of virtual devices configured from the plurality of disk drives, the disk controller comprising: a channel adapter configured to connect a host computer via a channel; a disk adapter configured to access a predetermined storage region of the logical device; a cache memory configured to transmit and receive data between the channel adapter and the disk adapter; a compression unit configured to carry out compression processing on the data; a power control unit configured to control power supplied to the plurality of disk drives, wherein the disk controller forms a logical device after a trial compression based on data compressed by the compression processing, and allocates the logical device after the trial compression to at least one of the plurality of virtual devices, wherein the power control unit is configured to stop the power supplied to disk drives of the plurality of disk drives which are configuring virtual devices to which the logical device is no longer allocated after the trial compression; and a service processor configured to: estimate, prior to compression being executed on a logical device, an estimated performance of the logical device after compression; compare the estimated performance with an access frequency of the logical device; and determine whether or not to execute compression for the logical device based on the comparison of the estimated performance with the access frequency of the logical device.