A system for performing efficient backup in an environment where a plurality of file servers exist, making the plurality of file servers externally look like a single apparatus. The present invention provides a computer system comprising hosts, first and second file servers connected to the hosts, and a storage system connected to the first and second file servers. The second file server determines that a file as a backup object is managed by the first file server, and notifies the first file server of an instruction of backup. In response to this instruction, the first server sends the second file server an identifier of a storage device that stores duplicate data of the file in question. Based on the received identifier, the second file server sets a path to that storage device, and obtains the backup data from that storage device.