Device boxing

In certain error recovery situations and in response to certain commands, the MVS™ system can “box” an I/O device. Once a device enters a boxed state, the system:

Immediately terminates I/O in progress on the device
Rejects future I/O requests (by a user or by the system) to the device as permanent I/O errors
Rejects any attempts to allocate the device
Puts the device in pending-offline status

The system boxes a device:

When it detects hot I/O on the device and the device cannot be recovered
When, because of a channel path error, it takes the last path to the device offline
When, because of a channel path error, it releases a reserve or assign on the device
When it releases an unconditional reserve for the device
When you issue a VARY OFFLINE command with the FORCE option for the device
When you issue a CONFIG OFFLINE command with the FORCE option for a channel path, and the command releases a hardware reserve or assign, or removes the last path to the device

Note:

Because you might release a reserve or assign on a device and cause a data integrity exposure, be sure to use the VARY OFFLINE and CONFIG OFFLINE commands with FORCE only in emergency situations.
When you fix whatever caused the system to box a device, you can take the device out of the boxed state at any time by issuing VARY device ONLINE. Once the VARY command takes effect, the device is again available for IOS and any subsequent allocations (i.e., an allocation done in another step or job, or another dynamic allocation). Note that after the VARY command takes effect, the device is not considered for the current allocation.
You can make a boxed alias unit control block (UCB) of a parallel access volume available using the DEVSERV, QPAVS command.
You cannot take a boxed device out of the boxed state by replying with the device name to the allocation recovery message, IEF238D.