Patent ID: 7506120

Claim:
A method of controlling data transfer in a virtualization system, the virtualization system coupled to a host system and a plurality of storage systems and having a virtual volume related to a first logical volume, the first logical volume being related to a portion of disk drives in a first storage system of the storage systems, the method comprising: receiving a first input request, the first input request being sent from the host system and targeted to the virtual volume; transferring data of the first input request to the first logical volume, so that the first storage system inputs the data of the first input request into a storage area of the disk drives related to the first logical volume; copying data stored in the first logical volume to a second logical volume related to a portion of disk drives in a second storage system of the storage systems; starting to migrate data stored in the first logical volume to a third logical volume related to a portion of disk drives in a third storage system of the storage systems during the copying step; and processing a new input request targeting the virtual volume according to differential information that records locations for which data migration is completed in the first logical volume and the third logical volume when the virtualization system receives the new input request to the virtual volume from the host system during the migration step.