In a file system in which data is distributively stored on a plurality of volumes in compliance with file storage requests from business applications, the present invention calculates reliability requirements or performance requirements which represent storage requirements for the storage of individual files requested for storage, selects an actual file storage destination volume in accordance with the reliability characteristics or performance characteristics of each volume, and stores file data on the selected storage destination volume. Since the storage requirements are calculated to select a storage destination volume for each file, data storage destination optimization can be achieved on an individual file basis.