The data duplication system comprises a first storage device having a first data protection area for storing backup images of multiple generations of a first volume for data read/write by an external device. The first data protection area is inaccessible to the external device. A second storage device coupled to the first storage device. The first storage device creates a second volume for storing a backup image of a particular generation of the plurality of generations of backup images stored in the first data protection area. The second storage device creates a third volume for storing the copy data, and a virtual volume that is mapped to the second volume of the first storage device. The second storage stores the backup data of a specific generation stored in the second volume in the third volume via the virtual volume by forming a pair that copies the data in the virtual volume and the third volume.