Patent ID: 8375168

Claim:
A storage system comprising: a first storage system including a plurality of first disk drives and a first controller managing a plurality of first logical units on said first plurality of disk drives in said first storage system; a second storage system including a plurality of second disk drives and a second controller managing a plurality of second logical units on said second plurality of disk drives in said second storage system; a first device being adapted to be coupled to said first storage system, managing said plurality of first logical units in the first storage system and providing a third logical unit to a host computer; a second device being adapted to be coupled to a said second storage system, managing said plurality of second logical units; wherein said first storage device and said second device are adapted to control write data received from the host computer to said third logical unit so as to be written to both a fourth logical unit included in said plurality of first logical units of the first storage system and fifth logical unit included in said plurality of second logical units of said second storage system.