When there is an access passing between unit disk controllers, the band of a mutual connecting network must be very large in order to exhibit the performance sufficiently, so that the cost is increased. In the present invention, the access number of a logical volume is monitored, the change of an access path is suggested to an upper class device, and the logical volume is moved or copied to each unit disk controller, so that the mutual connecting network is used mainly for copy of the logical volume, thereby reducing the necessary band.