The computer system comprises a first and second computer, at least one first storage system connected to the first computer, and a plurality of second storage systems connected to the second computer as well as being connected to the at least one first storage system. The first computer issues to the first storage system a normal write request and control-use write request stamped with issue time. A control-use write request is issued at periodic intervals. The first storage system receives a write request and transmits the write request as update-data to second storage system in such a way that the issue order is ascertainable. The second storage system receives the update-data and, responsive to a reflect instruction from the second computer, reflects the update-data in storage areas. The second computer acquires the issued times stamped on update-data received by the second storage systems, establishes a standard time on the basis of issue times, and instructs the plurality of second storage systems to reflect the update-data whose issue time is at or prior to the standard time in storage areas.