Patent ID: 7421435

Claim:
A storage system comprising: a first disk array system coupled to a host computer including: a plurality of first disk drives; a first volume related to a first portion of tile first disk drives and set as a primary volume; a second volume related to a second portion of the first disk drives; a third volume related to a third portion of the first disk drives; and a first controller storing update data sent from the host computer in the first volume, second volume, and third volume, and transferring both the update data stored in the second volume and the update data stored in the third volume; a second disk array system coupled to the first disk array system including: a plurality of second disk drives; a fourth volume related to a first portion of the second disk drives and set as a first secondary volume; and a second controller receiving the update data stored in the second volume, from the first disk array system according to an asynchronous remote copy procedure, and storing the update data received from the first disk array system in the fourth volume; and a third disk array system coupled to the first disk array system including: a plurality of third disk drives; a fifth volume related to a first portion of the third disk drives and set as a second secondary volume; and a third controller receiving the update data stored in the third volume from the first disk array system according to an asynchronous remote copy procedure and storing the update data received from the first disk array system in the fifth volume, the second disk array system includes a sixth volume related to a second portion of the second first drives and temporarily stores update data received from the first disk array system in the sixth volume before storing it in the fourth volume; the third disk array system includes a seventh volume related to a second portion of the third disk drives and temporarily stores the update data received from the first disk array system in the seventh volume before storing it in the fifth volume; the update data stored in the second volume is appended to first update information; the update data stored in the third volume is appended to second update information; if the update data stored in the sixth volume is stored in the fourth volume, the first update information is used to record a sequence of updates from the host computer; and if the update data stored in the seventh volume is stored in the fifth volume, the second update information includes common information included in the first update information used to record the sequence of updates from the host computer.