Traffic reducing on data migration

A first storage system in a system of a plurality of storage systems, the first storage system comprising a processor;

• a memory;
• and a migration control module, the migration control module being configured to:
• migrate a set of source primary and secondary volumes from the first storage system to one or more target storage systems by managing and copying, between the first storage system and the one or more target storage systems, a plurality of same data and a plurality of difference data between the source 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 source primary or secondary volume associated with the difference data;
• wherein each source secondary volume which corresponds to a source primary volume, if said each source secondary volume contains data, has a same data as the source primary volume and, if said each source secondary volume is not synchronized with the source primary volume, further has a difference data with respect to the source primary volume.

A second storage system in a system of a plurality of storage systems, the second storage system comprising a processor;

• a memory;
• and a migration control module, the migration control module being configured to:
• migrate a set of source primary and secondary volumes from one or more source storage systems to the second storage system by managing and copying, between the one or more source storage systems to the second storage system, a plurality of same data and a plurality of difference data between the source 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 source primary or secondary volume associated with the difference data;
• wherein each source secondary volume which corresponds to a source primary volume, if said each source secondary volume contains data, has a same data as the source primary volume and, if said each source secondary volume is not synchronized with the source primary volume, further has a difference data with respect to the source primary volume.