Patent ID: 8645645

Claim:
A file management method of a file server having a storage system having first and second volumes, comprising: initializing the first volume as a first file system; initializing the second volume as a second file system; wherein the first file system and the second file system represent a real file system; defining a pseudo file system virtually and hierarchically integrates the first file system and the second file system; storing management information for each of the files managed in a hierarchical file group, the first file system or the second file system in which each of the file is stored and an identifier of file management information of each corresponding file, accessing to the first or second file system based on the management information when the server receives an access request specifying one file system of the hierarchical file group from the client computer; specifying a file to be subjected to a migration move in the hierarchical file group; and copying data of the file of the first file system corresponding to the file to be moved, from the first file system to the second file system, changing the management information regarding the file to be moved while maintaining a file name in the correspondence information in the second file system, where the file name is a complete path name used in the first file system for the file, and then deleting the file from the first file system, in response to a read request of the first file, access to the second file system by making reference to the management information, read the first file stored in the second file system and transfer the read first file as a response to the read request without first storing the read first file.