Enabling MIA DEVSEL24 and DEVSEL78 Tracing to Identify Tape Device Elimination
Article ID: 22192
Updated On:
Products
Issue/Introduction
Occasionally, MIA customers contact Support with questions regarding Tasks that have entered Tape Device Allocation Recovery when there appear to be online, unallocated devices on the Eligible Device List for that task that could have been selected for the allocation request.
Environment
Release: 12.5; 12.1
Component: MIA
Cause
Tape Devices can be eliminated from consideration for an allocation request for many reasons. For example, in a Tape Robotic environment, devices in one Silo can be eliminated from the EDL for a request by the software controlling the Robot if the Tape Volume required for the allocation resides in another Silo.
MIA can also eliminate Tape Devices from the Eligible Device List for an allocation request. MIA performs Tape Device Elimination in three ways:
- MIA unconditionally eliminates OVERGENNED devices from the OFFLINE Device List in Allocation Recovery. It can also eliminate Overgenned Devices from the Eligible Device List during Allocation, if SETOPTION TPCF OVGINELIG=YES has been set.
- CA MIA can eliminate devices from the Eligible Device List if CA MIA JOBRESERVE is in effect. In this case, MIA will eliminate devices that have been reserved for other TASKs via the MIA VARY JOB= command. If MIA Device Elimination due to JOBRESERVE would, in effect, eliminate ALL devices from the EDL for an allocation request, MIA will restore the EDL to it's pre-JOBRESERVE elimination state, allowing the task to allocate a device.
- CA MIA allows Users to code their own Tape Device Elimination logic via USER Exit TPCEDLXT. If the User supplied logic were to cause the elimination of all devices from the EDL for the allocation request, MIA would restore the EDL to its pre-USER Exit elimination state, allowing the task to allocate a device.
Since MIA Tape Device Elimination occurs without any outward diagnostics or messages indicating why a particular device or devices were eliminated from consideration for an allocation request, CA MIA provides two traces to identify why MIA has performed Tape Device Elimination. The DEVSEL24 trace identifies any Tape Device Elimination performed by MIA when it processes the SSI #24 Common Allocation Call. The DEVSEL78 trace identifies any Tape Device Elimination performed by MIA when it processes the SSI #78 Tape Device Preferencing call. These two Subsystem Interface calls are issued by z/OS to allow any interested parties, such as MIA and other Tape related software, an opportunity to influence Tape Device selection.
In addition, the MIA DEVSELxx traces identify the contents of the original EDL, as well as the state of the EDL at the time that MIA received it. This can help to identify Tape Device Elimination that is occurring before MIA ever receives control of it.
Resolution
The Traces can be set dynamically via the MIM SETOPTION commands for this:
F MIM,SET TRACE=ON
F MIM,SET TPCF SETTRACE=DEVSEL24 F MIM,SET TPCF SETTRACE=DEVSEL78
To disable the traces once the problem has occurred and been captured, issue:
SET TRACE=OFF
The trace output will be sent to the location specified by the //MIMTRACE DD in the start-up proc for the task. When run for extended periods of time, these traces can create large volumes of output. If the problem is not easily recreatable, it may be desirable to send the output to a SYSOUT class. If a SYSOUT dataset is used, and the problem has not occurred recently, the following command can be used to close the current data set and open a new data set so that the unneeded trace data can be purged from the spool:
SET TRACE=(SPIN,CLASS=c)
In the above command, 'c' should be replaced with a valid SYSOUT class.
Note that the first dataset created on a spool is not deletable until the task is stopped. It is recommended the spin command be issued immediately after starting the trace, so that the size of the first file remains relatively small. And, subsequent datasets can be closed and deleted whenever necessary.
Additional Information
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