Patent ID: 8219748

Claim:
A storage system, comprising: a plurality of RAID groups which are configured by two or more physical storage devices included in a plurality of physical storage devices; a spare physical storage device; and a controller which sets respective physical storage devices to a power-saving state, the physical storage devices which are able to respond to a first prescribed type of command in the power saving state, wherein the controller sends the first prescribed type of command to respective physical storage devices that are in the power-saving state at a first time interval without canceling the power-saving state of the respective storage device, and then checks a first response to the first prescribed type of command from the respective physical storage devices in the power-saving state; if the controller receives the first response to the first prescribed type of command from the respective physical storage devices, the controller maintains the power-saving state of the respective physical storage devices in the power-saving state, if the controller does not receive the first response to the first prescribed type of command from the respective physical storage devices in the power-saving state, then a power-saving diagnostic section cancels the power-saving state of physical storage devices configuring a first RAID group in which the physical storage device, from which the first response is not returned, is included, reads out data from the physical storage devices configuring the first RAID group, and stores either the read data or data obtained by performing a prescribed operation using this read data in the spare physical storage device, wherein the controller cancels the power-saving state of respective physical storage devices that are in the power-saving state, sends a second prescribed type command to the respective physical storage devices for which the power-saving state has been canceled at a second time interval which is a longer time interval than the first time interval and checks a second response to the second prescribed type command from the respective physical storage devices; and if the second response to the second prescribed type of command is not returned, the controller reads data from physical storage devices configuring a second RAID group in which an unresponsive physical storage device is included and stores either the read data or data obtained by performing the prescribed operation using this read data in the spare physical storage device.