Patent ID: 8484425

Claim:
A storage system comprising; an external storage device including a plurality of external physical storage devices and an external storage controller being configured to manage an external logical volume on the external physical storage devices; a first virtualization device coupled to a computer and the external storage device, and being configured to provide a first logical volume, which includes a first virtual storage area mapped to all or a part of a storage area of the external logical volume provided by the external storage device, to the computer through a first port and a second port; and a second virtualization device coupled to the computer and the external storage device, and begin configured to provide a second logical volume to the computer through a third port, wherein the second logical volume includes a second virtual storage area mapped to the all or the part of the storage area, which is also mapped to the first virtual storage area in the first logical volume, of the external logical volume, wherein a first path is defined between the first logical volume and the computer through the first port, a second path is defined between the first logical volume and the computer through the second port, and a third path is defined between the second logical volume and the computer through the third port, wherein at a point in time during which the first virtualization device provides the first logical volume by a first identification number of the first logical volume and a first port number of the first port to the computer by the first path, the first virtualization device also provides the first logical volume by the first identification number of the first logical volume and a second port number of the second port to the computer by the second path, and the second virtualization device also provides the second logical volume by a second identification number of the second logical volume and a third port number of the third port to the computer by the third path, and wherein first identification number is the same as the second identification number and the first, second and third port numbers are different from each other.