disk array device and CONTROL METHOD disk array device

This invention relates to a disk array device and a one control method. Times at which data read requests from a logical volume (83) or writing data therein is received are stored as access time of a RAID group. When a predetermined time has elapsed after the access time, some hard disk drives (80) are set to an energy saving mode. There are the first hard disk drive (80) and second hard drives have a shorter lifespan. When the RAID group consists only of the first units, some first units are set to a power saving mode and when it consists only of second units, an arbitrary number of second units are established in a saving mode energy.