A controller discriminates the abnormality between a plurality of disk devices and a transmission path in a storage system having controllers for controlling a plurality of disk storage devices. When one controller in pairs of controllers for controlling the plurality of disk storage devices detects an error during an access to a disk drive of interest, a dummy access is made to the disk drive concerned from a controller connected to another transmission path different from the transmission path. Or, an access is made thereto from another initiator of the transmission path, via the transmission path. Then, from the above access result, a suspected fault location is identified.