IBM Support

Apparent hang or loop during DFSMShsm shutdown or periodically

Question & Answer


During DFSMShsm shutdown processing consolidation of SMF type 30 records can cause the appearance of a loop condition. CPU usage is evident. The loop or hang can also exhibit itself periodically during the SMF INTERVAL time frames throughout the day,


Excerpt from MVS Init and Tuning for DDCONS:
ddcons { (yes)}
{ (no) }
Specifies whether duplicate EXCP entries for type 30 SMF records are to
be consolidated. When DDCONS(YES) is specified, SMF merges the EXCP
count for these duplicate entries into one entry if the following information is the same: - ddname
- Device class
- Unit type
- Channel address
- Unit address
Long-running jobs might take a long time to end in this case, because of
the building of the SMF type 30 records for a long-running job.

An indication of SMF consolidation would be an SRB mode loop in module IEEMB836 in the system trace table from a dump taken during the apparent loop condition.

Pros of DDCONS(YES):
Less SMF Type 30 records overall
Less SMF filling/swapping
Cons of DDCONS(YES):
Takes more CPU time and usage during HSM shutdown
Takes more CPU time and usage during SMF consolidation intervals
Pros of DDCONS(NO):
Faster HSM shutdown
Less likelyhood of periodic slowdowns
Cons of DDCONS(NO):
Lots more SMF type 30 records
Higher SMF filling/swapping rates
The option of specifying NODETAIL and INTERVAL in the SYS1.Parmlib
SMFPRMxx member would cause the EXCP section not to be written out to
the Type30 subtype4 and subtype5 records, but it would still write the
info out in Type30 subtype2 and subtype3 records. The difference in
subtypes with the INTERVAL parameter is that the subtype2 and subtype3
records are written out after each interval while the subtype4 and
subtype5 data is retained in the address space. With both NODETAIL
and INTERVAL, the tables are emptied at the interval rate, so growth
and slowdown does not happen.


Change the parameter to DDCONS(NO) in the SMFPRMxx member of SYS1.PARMLIB
and/or Shorten the INTERVAL parameter.

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Document Information

Modified date:
03 September 2021