Patent ID: 7725650

Claim:
A storage system having a plurality of data storage devices and a controller configured to control a data read/write operation to/from the data storage devices in response to a request from a host connected to the controller via a communication path, the storage system comprising: a virtual volume the host accesses; and a pool comprised of the data storage devices and allocated to the virtual volume when the controller controls the data write operation in response to the request from the host to the virtual volume, and when the controller controls the data write operation in response to the request from the host to the virtual volume, wherein, the controller is configured to put one or more of the data storage devices in the pool that are not allocated to the virtual volume in a standby mode, and to put the data storage devices in the pool that are allocated to the virtual volume in an operational model, a control table including allocation information of the data storage devices to the virtual volume, power supply information for the data storage devices, and information about a threshold percentage of data storage devices that are to be powered ON before being allocated to the virtual volume, wherein the controller is configured to calculate a current percentage of data storage devices that are powered ON before being allocated to the virtual volume, wherein the controller is configured to compare the information about the threshold percentage of data storage devices that are to be powered ON before being allocated to the virtual volume in the control table to the current percentage of data storage devices that are powered ON before being allocated to the virtual volume, and wherein, when the current percentage is less than the information about the threshold percentage of data storage devices in the control table, the controller is configured to power ON one or more storage devices before receiving a write request.