When a system, for example system A, is sharing devices with other systems, events on any one system can affect the ability of any or all the systems to access the shared devices. For example, if one of the sharing systems has an allegiance to a shared device, an I/O operation from system A to that device will receive a device busy condition. In this case, the I/O operation is held in system A's channel subsystem until the other system ends its allegiance. At that time, system A's I/O to that device can then be processed normally.
However, a problem either on the system that has the allegiance or in the I/O hardware could result in the allegiance not being freed. This could prevent the processing of any pending I/O operations from any of the sharing systems to the device(s) affected by the allegiance. The indication to any sharing systems that had an I/O operation hung by such a condition would normally be message IOS071I, indicating a start pending to the device.