Patent ID: 8099622

Claim:
A method of controlling a plurality of file systems, said plurality of file systems includes a first, second, and third file system, said plurality of file systems are clustered and has a single namespace, comprising: establishing a mirroring relationship between the first file system and the third file system, wherein a copy of the first file system is replicated to the third file system; creating a first referral on the second file system, wherein an access request from a client computer directed to the second file system for accessing a file stored in the first file system is directed to the third file system by the first referral whereby the copy of the first file system is accessed; directing access from said client computer to the third file system after the first file system receives a failback request from a management server, wherein an IP address of the first file system is assumed by the second file system on which the first referral was created, wherein if said access from said client computer is read access, file is read from said third file system, and wherein if said access from said client computer is write access, data is written to said third file system and a replication of said data is written to the first file system, wherein a network of the third file system is separated from a network of the first and second file systems by a router.