Patent ID: 7188218

Claim:
A storage system comprising: a first disk array system, in a primary site, coupled to a host computer, and having a plurality of first disk drive units in which data are stored and a first controller which controls to store data sent from said host computer to a primary volume related to a portion of said first disk drive units; a second disk array system, in a remote site, coupled to said first disk array system, and having a plurality of second disk drive units in which data are stored and a second controller which receives data of said primary volume from said first disk array system by an asynchronous remote copy procedure and controls to store data received from said first disk array system to a secondary volume related to a portion of said second disk drive units; and a third disk array system, coupled to said first disk array system, and having a plurality of third disk drive units in which data are stored and a third controller which receives data of said primary volume from said first disk array system by a synchronous copy procedure and controls to store data received from said first disk array system to a third volume related to a portion of said third disk drive units; wherein said third dish array system comprises a first area and a second area, said first area storing information related to data of a plurality of write requests received from said first disk array system by said synchronous copy procedure during a first time period, wherein said second area storing information related to data of a plurality of write requests received from said first disk array system by said synchronous copy procedure during a second time period being different from said first time period, wherein said third disk array system stores information related to data of a plurality of write requests received from said first disk array system in said first area during said first time period and said second area during said second time period, and wherein said information stored in said second area is used to decide data to be transferred from said third disk array system to said second disk array system in the event of a disaster that affects said primary site.