Storage device system interfacing open-system host computer input/output interfaces

A storage device system in which migration of data from an existing storage device to a higher-standard storage device is unnecessary, and in which discarding of existing storage devices by the user can be prevented. A CHF receives a Read Capacity command from a new-type storage device (S). Using LDEV, LUN and other information tables, an LUN is converted into a mapped LDEV (S). A check is performed to determine whether the LDEV emulation type is read-only, write-only, or read/write (S). If none of these, a check is performed to determine whether the emulation type is newly created (S). If newly created, the size of all storage areas of the LDEV are set as the Max LBA in a response to the new-type storage device (S). If the result of S is YES, the size of the user area in the LDEV is set as the Max LBA in a response to the new-type storage device (S). If not newly created, processing proceeds to the processing of S