Patent ID: 7343461

Claim:
A storage system comprising: a first disk array system, adapted to be coupled to a host computer, and comprising a plurality of first disk drive units in which data are stored and a first controller which controls storing of data sent from said host computer to a primary volume related to at least a portion of said first disk drive units; a second disk array system, adapted to be coupled to said first disk array system, and comprising 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 storing of data received from said first disk array system to a secondary volume related to at least a portion of said second disk drive units; and a third disk array system, adapted to be coupled to said first disk array system, and comprising 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 remote copy procedure and controls storing of data received from said first disk array system to a third volume related to at least a portion of said third disk drive units, wherein said third disk array system is adapted to comprise a first bitmap and a second bitmap, said first bitmap storing information related to data of a plurality of write requests received from said first disk array system during a first time period, said second bitmap storing information related to data of a plurality of write requests received from said first disk array system during a second time period which is different from said first time period.