. "The IBM's DFSMS (Data Facility Storage Management Subsystem) is an example, which is described in detail in ???IBM SYSTEMS JOURNAL, Vol. 28, No. 1, 1989, pp. 77-103. [0004] The disk data of the I/O subsystem of the mainframe computer system having the above-mentioned management function can be backed up in a medium such as a magnetic tape or a magnetic tape library capable of storing a large quant" . . .