If one of the CHPIDs that the Virtual Devices are using is taken offline, CA Vtape interacts with the channel path recovery feature of the operating system to dynamically switch to the next available CHPID in the assigned list. As with all devices, when the last assigned CHPID goes offline, the affected Virtual Devices are boxed or fenced. If the Virtual Devices are in use, the affected jobs have to be canceled, at least one of the assigned CHPIDs has to be brought back online, CA Vtape has to be stopped and started, and the affected jobs have to be resubmitted.
The CHPID list is one directional. When the first CHPID in the list is taken offline, the Virtual Devices are failed over to the next CHPID in the list. When the second CHPID in the list is taken offline, the Virtual Devices are failed over to the third CHPID in the list. The fact that the first CHPID in the list may have been brought back online does not matter. Failover cannot go back to a CHPID previously used or wrap back to the first CHPID in the list when the last CHPID in the list is taken offline. Once CHPID failover has occurred, the failed CHPID can only be reused if CA Vtape is stopped and started.
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