In a storage system allowing redundant writing, a technology is provided capable of achieving control including efficient return to redundancy while reducing load on a host and trouble for a user. The host performs the redundant writing of data into data volumes in primary and secondary storage apparatuses. Each storage apparatus retains information including update data from the host as a journal (update data history information). When one of two systems for redundant writing is in a failed state and it is to be returned to a redundant state, the storage apparatuses communicate with each other regarding the journals not through the host. A retained portion of the journal of the normal system after the latest synchronization point required for synchronizing the volumes is transferred through data copy to the system to be recovered. Based on the transferred portion of the journal, the volume is restored and synchronized.