Patent ID: 7167963

Claim:
A storage system comprising; a first disk array system, at a first site, coupled to a host computer and having a first controller and a plurality of first disk drives, a first portion of said first disk drives being related to a first volume as a primary volume; a second disk array system, at a second site, coupled to said first disk array system and having a second controller and a plurality of second disk drives, a first portion of said second disk drives being related to a second volume; and a third disk array system, at a third site, coupled to said second disk array system and having a third controller and a plurality of third disk drives, a first portion of said third disk drives being related to a third volume as a secondary volume, wherein said first controller receives an update data sent from said host computer to said first volume and stores said update data in said first volume and stores copy data of said update data in a storage area in said first disk array system and transfers said copy data of said update data to said second disk array system based on a first copy process, wherein said second controller receives said copy data of said update data from said first disk array system and stores said copy data of said update data in said second volume based on said first copy process and transfers said copy data of said update data to said third disk array system based on a second copy process, wherein said third controller receives said copy data of said update data from said second disk array system and stores said copy data of said update data in said third volume based on said second copy process, wherein said first controller sends said copy data of said update data stored in said storage area to said third disk array system so that said storage system can continue to store data in said third volume based on a third copy process between said first disk array system and said third disk array system, if said second disk array system has a failure, wherein said first, second and third sites are different from each other, and wherein said storage area is a fourth volume related to a second portion of said first disk drives, said fourth volume being provided for temporarily storing said copy data of said update data before transferring.