Patent ID: 7117249

Claim:
A method of sharing data in a computer system, said computer system comprising a first computer, a second computer, and a storage system comprising a disk control unit, a first disk unit, a second disk unit, and a third disk unit, the method comprising: forming a first duplex state between said first disk unit and said second disk unit, wherein said disk control unit, in response to a write request from said first computer, stores write data associated therewith to both said first disk unit and to said second disk unit, wherein said disk control unit, in response to a write request from said second computer, stores write data associated therewith to said third disk unit; forming a simplex state and sending a first message from said first computer to said second computer indicating forming of said simplex state, wherein said disk control unit, in response to a write request from said first computer, stores write data associated therewith only to said first disk unit, wherein said disk control unit, in response to a write request from said second computer, stores write data associated therewith to said third disk unit; subsequent to receiving said first message performing at said second computer a re-mapping operation between said second disk unit and said third disk unit; and forming a second duplex state between said first disk unit and said third disk unit, wherein said disk control unit, in response to a write request from said first computer, stores write data associated therewith to both said first disk unit and to said third disk unit, wherein said disk control unit, in response to a write request from said second computer, stores write data associated therewith to said second disk unit.