Disaster backup facilities

To provide disaster backup, two things are necessary: (1) a way to make copies of DFSMShsm-owned tape volumes and to identify the copied volumes to DFSMShsm; and (2) a way to cause DFSMShsm to use the copied volumes instead of the original volumes. To fulfill these needs, DFSMShsm provides the duplex tape option or the TAPECOPY command, and the TAPEREPL command.