A disk array has storage regions provided to store the management information for each disk volume of the backup data, and an interface is provided through which the management information for each disk volume is read from and written in by an external computer so that the backup data of disk volumes can be associated with the management information. The management information includes backup creation date and time, and content identifier, and it is set from the external computer, and updated according to the operations such as restore and tape copy based on the command from the external computer.