Patent ID: 7383264

Claim:
A data control method for duplicating data in a system which includes a primary system including a first computer system and a first storage device connected to said first computer system, and a secondary system including a second computer system and a second storage device connected to said second computer system, wherein at least said first storage device and said second storage device are connected to each other, said data control method comprising the steps of: into a disk drive within said first storage device, registering a log, stored in said first storage device, that can be used to generate an update of data, said data being produced as a result of processing performed by said first computer system and being stored in said first storage device; copying said log registered in said disk drive within said first storage device to a disk drive within said second storage device, said disk drive within said second storage device being set to duplicate said log; updating said data stored in said first storage device, said data being produced as a result of said processing performed by said first computer system; notifying said second computer system of a change in data stored in said disk drive within said second storage device, said change being made as a result of performing said copying step; reading said change in said data stored in said disk drive within said second storage device, this step being performed by said second computer system; and updating a duplicate of said data, stored in said first storage device, based on a log read by said second computer system, said duplicate of said data being stored in said second storage device.