Abstract: The present invention makes it possible to execute file management efficiently even if a situation occurs that real data cannot be acquired because metadata in a lower level system cannot be accessed. In a hierarchical storage system, a higher level system acquires available metadata range information indicative of available and unavailable ranges of metadata, from the lower level system, and identifies inaccessible files that are in a state that reading of substantial data in accordance with a stub file is impossible on the lower level, on the basis of the available metadata range information. The higher level system manages this inaccessible file information to transmit the information to a client computer or use the information to control a file access request from the client computer (see FIG. 9).