The present invention provides a storage unit system that can be connected to a plurality of different kinds of networks and a controlling method for a system LU of a storage device control unit required in such a storage unit system. In the storage unit system, to an LDEV of a storage device, it is possible to set a system LU for storing control information in the storage unit system itself and a user LU for writing write data sent from a host device, while a management terminal specifies a system LU or a user LU to set a path definition to the LDEV and a CHN inhibits an access to the system LU from the host device in accordance with distinction specified by the management terminal. Furthermore, a path of the system LU is automatically defined to a backup LU, so that the control information stored in the system LU is backed up to the backup LU.