Database duplication method of using remote copy and database duplication storage subsystem thereof

A data duplication control method for a system which includes a main system having a first processor system in which a first DBMS operates and a first storage subsystem connected to said first processor system and a subordinate system having a second processor system in which a second DBMS operates and a second storage subsystem connected to said second processor system, with said first and second storage subsystems being connected to each other, said method comprising,

• a step, which is implemented by said first DBMS by being directed by said first storage subsystem, of overwriting DB table data which is stored in a cache and put in and out by said first DBMS to the DB table of said first storage subsystem, and holding the updating of the DB table data in the DB table against a subsequent request of updating of the DB table data, and
• a step, which is implemented by said first storage subsystem, of transferring and copying the DB table data of the DB table of the self storage subsystem to the DB table of said second storage subsystem thereby to duplicate the DB table data, and suspending the subsequent transfer of DB table data so that the DB tables of said first and second storage subsystems are in a state of matching,
• thereby enabling said second DBMS to refer the copied DB table in a state of matching.

A duplicated storage subsystem which includes a first storage subsystem having a first external storage control unit and a first external storage unit and is connected to a first processor system, and a second storage subsystem having a second external storage control unit and a second external storage unit and is connected to a second processor system, with said first and second external storage control units being connected to each other, wherein said first external storage control unit includes means of overwriting data, which is held in a cache of said first processor system, to said first external storage unit;

• means of holding the updating of the data which has been written to said first external storage unit against a subsequent request of updating;
• means of transferring the data to said second storage subsystem thereby to duplicate the data;. and means of suspending the subsequent transfer of data from said first external storage unit to said second storage subsystem, so that the data stored in said first and second storage subsystems are in a state of matching.