Patent ID: 8307158

Claim:
A storage system coupled to a host computer comprising: a plurality of first hard disk drives (HDDs) on which a first internal logical volume is configured; a plurality of second HDDs on which a second internal logical volume is configured; and a controller being configured to control said plurality of first HDDs as a first error check and correction (ECC) group, and control said plurality HDDs as a second ECC group, and to provide a first logical volume associated with said first internal logical volume; wherein said controller is configured to write data, which is requested to write to said first logical volume by the host computer, to said associated first internal logical volume, and wherein said controller is configured to switch association between said first logical volume and said first internal logical volume to association between said first logical volume and said second internal logical volume, and then stop power supply to said plurality of first HDDs on which said first internal logical volume is configured.