Patent ID: 8832397

Claim:
A storage system comprising: a first external storage device including a plurality of external physical storage devices and a controller configuring a first external logical volume on the external physical storage devices; a second external storage device including a plurality of external physical storage devices and a controller configuring a second external logical volume on the external physical storage devices, where data stored in the first external logical volume is duplicated to the second external logical volume; a first virtualization device coupled to a computer and the first external storage device, and providing a first logical volume, which corresponds to storage areas of the first external logical volume, to the computer; and a second virtualization device coupled to the computer and the second external storage device, and providing a second logical volume, which corresponds to storage areas of the second external logical volume, to the computer, wherein the same identification number is used by the computer for accessing the data stored in the first external logical volume via the first logical volume and for accessing the data stored in the second external logical volume via the second logical volume.