A storage system has a controller and a plurality of storage devices connected to a pair of loops, the controller diagnoses storage devices and performs automatic high-speed restoration of the loops. A storage system has a controller, a plurality of storage devices, and switch circuits having a plurality of switches to connect each of the plurality of storage devices to loops. When a loop anomaly is detected, a restoration instruction is issued to a switch circuit, the plurality of switches are operated in parallel, storage devices are diagnosed, and according to the diagnosis results, a storage device judged to be anomalous are bypassed from the loop by operating the switches. When a loop anomaly is detected, diagnosis of the disk drives connected to the loop can be performed in parallel, so that the time until automatic restoration of the loop can be greatly reduced.