Exemplary embodiments provide a technique to reduce the traffic between storage devices during data migration. In one embodiment, a system comprises a plurality of storage systems which are operable to migrate a set of primary and secondary volumes between the storage systems by managing and copying, between the storage systems, a plurality of same data and a plurality of difference data between the primary and secondary volumes and location information of each of the plurality of difference data, the location information identifying a location of the difference data in the primary or secondary volume associated with the difference data. Each secondary volume which corresponds to a primary volume, if said each source secondary volume contains data, has a same data as the primary volume and, if said each secondary volume is not synchronized with the primary volume, further has a difference data with respect to the primary volume.