Computer system and data sharing method between computers

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, a third disk unit, and a fourth disk unit, the method comprising:

• forming a 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 fourth disk unit;
• forming a simplex state and sending a 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;
• subsequent to receiving said first message, copying data stored in said second disk unit to said third disk unit and then performing at said second computer a re-mapping operation between said third disk unit and said fourth disk unit, wherein subsequent to said re-mapping said disk control unit accesses said third disk unit in response to I/O requests from said second computer;
• and
• re-forming said duplex state between said first disk unit and said second disk unit, wherein said disk control unit, in response to a subsequent write request from said first computer, stores write data associated therewith to both said first disk unit and to said second disk unit.

A method of sharing data in a computer system, said computer system comprising a first computer, a second computer, a first storage system coupled to said first computer and comprising a first disk unit and a first disk control unit, and a second storage system coupled to said second computer and comprising a second disk unit, a third disk unit, a fourth disk unit, and a second disk controller unit, wherein said first disk control unit and said second disk control unit are coupled via a network, the method comprising steps of:

• forming a duplex state between said first disk unit and said second disk unit, wherein said first 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 second disk control unit, in response to a write request from said second computer, stores write data associated therewith to said fourth disk unit;
• terminating execution of applications in said first computer;
• subsequent to said terminating, forming a simplex state, wherein said first disk control unit, in response to a write request from said first computer, stores write data associated therewith only to said first disk unit;
• subsequent to said step of forming a simplex state, sending a message from said first computer to said second computer indicating said simplex state, wherein said second computer performs copying data stored in said second disk unit to said third disk unit and subsequent to said copying, performs a re-mapping between said third disk unit and said fourth disk unit so that said second disk control unit now accesses said third disk unit, in response to I/O requests from said second computer;
• and
• re-forming said duplex state between said first disk unit and said second disk unit, wherein said disk control unit, in response to a subsequent write request from said first computer, stores write data associated therewith to both said first disk unit and to said second disk unit.

A storage system comprising:

• a disk control unit;
• and
• a plurality of disk units,
• wherein said disk control unit is operable to form a duplex state between a first disk unit and a second disk unit, wherein data associated with a write request from a first computer is stored to both said first disk unit and to said second disk unit, wherein a third disk unit is accessed to service an I/O request from a second computer,
• wherein said disk control unit is further operable to form a simplex state between said first disk unit and said second disk unit, wherein data associated with a write request from said first computer is stored only to said first disk unit,
• wherein during said simplex state, an application executing on said first computer sends a message to said second computer indicating forming of said simplex state, wherein data stored in said second disk unit is copied to a third disk unit,
• wherein subsequent to data being copied from said second disk unit to said third disk unit, a re-mapping of said second disk unit and said third disk unit is performed so that said second disk unit is accessed to service subsequent I/O requests from said second computer,
• wherein another duplex state is formed between said first disk unit and said third disk unit so that data associated with subsequent write requests from said first computer are stored to both said first disk unit and to said third disk unit.

A storage system comprising:

• a disk control unit;
• and
• a plurality of disk units,
• wherein said disk control unit is operable to form a duplex state between a first disk unit and a second disk unit, wherein data associated with a write request from a first computer is stored to both said first disk unit and to said second disk unit, wherein data associated with a write request from a second computer is stored to a fourth disk unit,
• wherein said disk control unit is further operable to form a simplex state, wherein an application executing on said first computer sends a message to said second computer indicating forming of said simplex state, wherein data associated with a write request from said first computer is stored only to said first disk unit,
• wherein during said simplex state, data stored in said second disk unit is copied to said third disk unit and subsequent to said copying, data associated with a write request from said second computer is stored to said third disk unit as a result of a re-mapping performed between said third disk unit and said fourth disk unit,
• wherein said duplex state is re-formed between said first disk unit and said second disk unit.

A storage system comprising:

• a disk control unit;
• a plurality of disk units;
• and
• a network connecting at least some of said disk units,
• said disk control unit being operable to copy data stored in a first disk unit to a second disk unit via said network,
• said disk control unit being operable to form a duplex state between said first disk unit and said second disk unit, wherein data associated with a write request from a first computer is stored to both said first disk unit and to said second disk unit, wherein data associated with a write request from a second computer is stored to a third disk unit,
• said disk control unit further being operable to form a simplex state, wherein an application executing on said first computer sends a message to said second computer indicating forming of said simplex state, wherein data associated with a write request from said first computer is stored only to said first disk unit,
• wherein during said simplex state, data stored in said second disk unit is copied to a third disk unit and, subsequent to said copying, said second computer accesses said second disk unit as a result of a re-mapping performed between said second disk unit and said third disk unit,
• wherein another duplex state is formed between said first disk unit and said third disk unit so that data in subsequent write requests from said first computer are stored in both said first disk unit and said third disk unit.