Patent ID: 8583611

Claim:
A system comprising: a file server managing a plurality of files, the file server including a CPU and a memory; a local storage device coupled to the file server, the local storage storing at least some of the files; a plurality of first file storage systems coupled to the file server, each of which including a first file server and a first storage device; and a plurality of second file storage systems coupled to the file server, each of which including a second file server and a second storage device, wherein the memory stores: file management information including, for each of files, access control information and last access time, and storage management information including, for each of the first and the second file storage systems, its I/O performance and information indicating whether high or low of its credibility determined by its difficulty for a leak of information and a falsification of information, wherein a high credibility has a greater credibility than a low credibility, wherein the credibility information of the first file storage systems is high and the credibility information of the second file storage systems is low, wherein the file server is configured to: determine one of the files to migrate in accordance with both I/O performance of the local storage device and access status to the files, and when importance of the file to migrate is high which is determined by the access control list of the file, select one of the first file storage systems as a migration destination, and otherwise, select one of the second file storage systems as the migration destination, wherein a file with high importance has a greater importance than a file with low importance, wherein the one of the first or the second file storage systems as a migration destination is selected further based on the access status of the each of the files to be migrated and the I/O performance of the one of the first or the second file storage systems.