A computer system comprises a storage subsystem, a host computer and a management computer, and stores catalogue information containing correspondence between a first volume for data reading or writing and a second volume for storing a copy of the data stored in the first volume. The management computer requests the storage subsystem to erase the data stored in the first volume upon reception of an erasure request of the data stored in the first volume. The storage subsystem erases the data stored in the first volume. The management computer specifies a second volume for storing the copy of the data stored in the first volume based on the catalogue information. The storage subsystem erases data stored in the specified second volume. Thus, security risks are reduced by erasing data regarding the data when the data stored in the volume is erased.