1. A file system migration method used in a storage system that includes a plurality of servers and a disk subsystem connected to the plurality of servers, and has all or a part of at least one file system stored in a logical device of the disk subsystem, comprising: referencing, in response to an instruction to execute migration of the file system from a first server to a second server out of the plurality of servers, a relation between the logical device of the disk subsystem and a logical unit used for the servers to recognize the logical device; sending an instruction to update the relation between the logical device and the logical unit to the second server; and causing the second server to newly recognize the logical unit, in response to the instruction to update, and update an identifier of the server managing all or a part of the file system.