Patent ID: 6950920

Claim:
A storage system coupled to a first computer and to a backup server, the storage system comprising: a plurality of disks which constitute a plurality of logical units; a first controller including a first cache memory and in data communication with the first computer; and a second controller including a second cache memory and in data communication with the backup server, wherein the first controller is operable to control a first logical unit pair including a first logical unit and a second logical unit, the second logical unit being a replication logical unit of the first logical unit, the first controller being configured to hold configuration information of the first logical unit and the second logical unit, wherein when the first logical unit pair is split: configuration information of the second logical unit is transmitted from the first controller to the second controller; data stored in the first cache memory is written into the second logical unit; and the first controller transfers control of the second logical unit to the second controller, wherein data stored in the second logical unit can be backed up to the backup server via the second controller and the first controller maintains control over the first logical unit”.