Storage system and method of controlling storage system

A method of controlling a storage system including a first physical storage apparatus providing a first real volume and a second physical storage apparatus providing a second real volume to form a copy pair with the first real volume, the method comprising:

• providing, by the first physical storage apparatus, a first host with a first storage identifier and a first virtual volume identifier for the first host to access the first real volume;
• providing, by the second physical storage apparatus, wherein the first storage apparatus and the second physical storage apparatus reside on different networks respectively, a second host with at least a part of a first virtual storage apparatus including a first virtual volume the second real volume is allocated;
• assigning, by the second physical storage apparatus, the first virtual volume identifier to the first virtual volume and the first storage identifier to the first virtual storage apparatus;
• and
• providing, by the second physical storage apparatus, the second host with the first storage identifier and the first virtual volume identifier for the second host to access the second real volume via the first virtual volume.