To allow other volumes to continue copy operation interrupted by a trouble quickly in a storage system having a software duplex volume and an asynchronous copy volume.

The storage system comprises at least two primary storages for processing a write request from a host device in parallel, and at least one secondary storage for receiving write data asynchronously with the write request from the storage for copying. The primary storage adds order information to the write request for transmitting to the secondary storage along with write data; the secondary storage holds the order information attached to data recorded on an own logical disk; and another primary device inquires the order information of data that have already been recorded in the secondary storage for succeeding data transmission to the secondary storage from the next write data, when the primary storage in charge of transmitting data to the secondary storage fails.