In the data processing system which maintains data duplication between sites having a host computer and a storage apparatus, transfer-data volume and cost in communication line between the sites are controlled and the load of both primary and secondary hosts is controlled, and a data update management function at the secondary site side is realized. In the primary site, a primary DKC of primary storage apparatus stores an update data in a primary side file when a primary user data is updated from a primary host. Being asynchronous with this update, a secondary remote copy program of a primary remote copy program and an intermediate processing section remote-copies and accumulates the update data in a secondary side file. A data reflection program of a secondary host reads the accumulated data and commands a secondary DKC of a secondary storage apparatus to reflect it on a secondary user data and stores the update information in a secondary log data.