When a device appears to be hung, an operator can consider varying the device offline to try releasing the hang condition at the device. However, the VARY OFFLINE command may obtain resources critical to the system and may attempt to issue I/O. Depending on the condition that caused the device to hang in the first place, this may cause the VARY OFFLINE command to also hang.
To avoid this problem, the operator can choose to use the VARY OFFLINE command with the FORCE parameter to mark the device offline and boxed. The FORCE parameter will not obtain resources or issue I/O, so it will complete regardless of any hardware problems with the device. Since the device is boxed, all I/O will be posted back to the I/O issuer in permanent error, which should cause all system resources previously held to be released.
See Boxed device - operator actions for more information on boxing devices. See VARY command for more information on the FORCE option.