Provided is a method including the steps of: storing multiple IP addresses and resource management information including correspondence relationships among the multiple IP addresses, multiple file cache regions and multiple virtual file servers; processing multiple file requests transmitted from a client computer in accordance with the resource management information, by use of a lent file cache region being a part of the multiple file cache regions corresponding to the multiple virtual file servers, a lent IP address being a part of the multiple IP addresses, and a lent volume being a part of multiple volumes, the requests transmitted by designating the multiple virtual file servers, respectively; and creating a child virtual file server by receiving a child virtual file server creation request designating one of the multiple virtual file servers.