A storage system includes a storage and control units. In each of the control units: a relay unit relays access to the storage; an access controller accesses the storage through one of the relay unit in the control unit and the relay unit in another of the control units; and an operational-state controller determines whether or not the relay unit in the above-mentioned another control unit is usable when the operational-state controller detects occurrence of an abnormality in the above-mentioned another control unit, and makes the above-mentioned another control unit transition to a partially-operational state when the relay unit in the above-mentioned another control unit is usable. In the partially-operational state, at least the access controller in the above-mentioned another control unit is not in operation and the access controller in the control unit can access the storage through the relay unit in the above-mentioned another control unit.