Patent ID: 7930500

Claim:
A storage system comprising: a first disk array system coupled to a host computer and having a first controller and a plurality of first disk drives, said first disk drives being related to a first volume as a primary volume and a second volume; a second disk array system coupled to said first disk array system and having a second controller and a plurality of second disk drives, said second disk drives being related to a third volume as a first secondary volume; and a third disk array system coupled to said first disk array system and having a third controller and a plurality of third disk drives, said third disk drives being related to a fourth volume as a second secondary volume; wherein said first controller receives an update data sent from said host computer to said first volume and stores a first data corresponding to said update data in said first volume and stores a second data corresponding to said update data in said second volume and transfers said second data to both said second disk array system and said third disk array system; wherein said second controller receives said second data from said first disk array system and storing said second data in said third volume; and wherein said third controller receives said second data from said first disk array system and storing said second data in said fourth volume.