US Patent 7724643 Recovery of duplex data system after power failure

A duplex data system performs a recovery process normally even in the event of an abrupt abnormal power failure. The duplex data system has a first storage device, a second storage device, and a control unit for duplicating data by storing the data in the first storage device and the second storage device. For duplicating the data, the control unit first writes the data into the first storage device and, after having completed the writing of the data into the first storage device, writes the data into the second storage device.