It is provided a computer system, comprising a server and first and second storage systems. The first storage system stores deduplicated data sharing at least a part of data with other data, shared data shared by a plurality of pieces of the deduplicated data, and first type data representing a type of the stored data including the deduplicated data and the shared data. The deduplicated data is associated with the shared data by a pointer to the shared data, and includes differential data indicating a difference from the shared data. The server creates second type data representing a type of the data stored in the second storage system from the first type data. The second storage system stores the shared data associated with the deduplicate data at a reading position before a position at which the deduplicated data is read in sequential reading and stores the second type data.