To reconfigure I/O devices, enter a VARY ONLINE/OFFLINE command at the console with master authority. For a VARY OFFLINE command for a device that is currently in use, the operating system marks the device ‘pending offline’. The operating system makes no further allocations to the device unless the volume mounted on the device is specifically requested.
Because vary offline processing cannot complete until a device is unallocated, either wait until the jobs using the device complete or cancel them.
Before reconfiguring a complex from single-image mode to physically-partitioned mode, complete or cancel any tape volume mounts for devices to be reconfigured. Then enter a CONFIG CHP(ALL,n),OFFLINE,UNCOND command.
If a tape mount is pending when the CONFIG command is entered, the tape drive(s) might not start after they are mounted and the system has been partitioned. Another way to avoid this problem is to enter a VARY device online command for the tape drive(s).