When storage controllers are added to a storage system to change the storage system from a configuration having only one storage controller to a configuration having plural storage controllers, or when storage controllers are removed from the storage system to change the storage system from a configuration having plural storage controllers to a configuration having only one storage controller, a controller-internal management-information memory controller carries out a copy process to copy management information from each of the storage controllers to a management-information-memory switch or vice versa at the same time as processing of read and write requests for access to the management information, made by a channel interface or a disc interface, in order to change storage locations of the management information while processing the read and write requests made by the host.