Patent ID: 8832025

Claim:
A file server which is a local file server that is coupled to a communication network to which is coupled to a remote file server managing a remote storage device and that manages a local storage device, the file server comprising: a first communication interface device which is coupled to the communication network; a second communication interface device which is coupled to a user terminal for sending an access request that is either a read request or a write request specifying a file, and which is configured to receive the access request from the user terminal; and a processor which is coupled to the first and second interface devices, wherein the processor is configured to: (A) transfer a file in the local storage device to the remote file server; (B) manage the transferred file as a migration target file; (C) not delete the migration target file from the local storage device even when the (B) is completed, and delete the migration target file from the local storage device when a certain length of time has passed from the last access time when free capacity of the local storage device falls below a specified threshold; (K) acquire, from the remote file server, upon receiving a write request with respect to a stub of the migration target file that has been deleted from the local storage device, a file managed by the remote file server which is the link destination identified from this stub; (L) store the acquired file in the local storage device; and (M) update the acquired file in accordance with the write request received in the (K); and release the stub when performing the (K).