Device boxing

In certain error recovery situations and in response to certain VARY and CONFIG commands, the MVS™ system can “box” an I/O device.

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 the operator issues a VARY OFFLINE command with the FORCE option for the device
When the operator issues a CONFIG OFFLINE command with the FORCE operand for a channel path and the command releases a hardware reserve or removes the last path to the 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