Data migration from an existing NAS to a new NAS and processing of access from a client are executed in parallel. A migration destination NAS inherits the host name and IP address of a migration source NAS. The network environment parameters of the migration source NAS are changed to different values. The migration destination NAS causes data to migrate from a migration source storage region, in which a shared file system of the migration source NAS is mounted, to a migration destination storage region. In a case where there is an access request from the client during data migration, the migration destination NAS selects one of the storage region in correspondence to the migration status of the requested data and provides that data. Data of a "not copied" status is provided from the migration source storage region. Data of a "copied" status is provided from the migration destination storage region.
CROSS-REFERENCES TO RELATED APPLICATIONS
This application is a Continuation of U.S. application Ser. No. 10/767,442 filed on Jan, 30, 2004 now U.S. Pat. No. 7,240,122. Priority is claimed based on U.S. application Ser. No. 10/767,442 filed on Jan. 30, 2004, which claims priority to Japanese Patent Application No. 2003-316291 filed on Sep. 9, 2003.
