The file storage system of the present invention comprises a first server including a first file system (FS), and a second server including a second FS. The first and second servers respectively store first and second difference management tables. Upon receiving a write request, the first server stores a difference of a first file in the first FS, updates the first difference management table, and sends, to the second server, a difference storage notification showing that the difference of the first file has been stored in the first FS. The second server receives the difference storage notification, and updates the second difference management table.