The present invention provides a method for guaranteeing a data consistency among a plurality of storages and sites, when data transfer is performed by asynchronous remote copying from a site including a plurality of storages. When writing is made into a first storage system or a second storage system, the storage system that received the writing transfers the write data to the other storage system within the site by synchronous remote copying. At this timing the first storage system gives the write data information for order assurance. Furthermore, the first or the second storage system transfers the write data and thus given information for order assurance to the third or the fourth storage system by asynchronous remote copying. Furthermore, the third or the fourth storage system which has received the write data transfers to the other storage system within the same site the write data and information for order assurance by synchronous remote copy.