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Abstract
Some workloads may experience an increase in I/O pending faults and poor performance may be observed.
Content
After loading TR12 (V7R4) or TR7 (V7R5), you may notice an increase in I/O pending faults in pools using an Expert Cache setting of *CALC. SQL workloads can experience degraded performance. APAR DT456038 provides the first fix for this issue and APAR DT456384 provides the complete fix for this issue.
We know performance concerns after a Technology Refresh raise questions. This guide gives clear answers and next steps.
Do the fixes require an IPL?
Yes
Who should apply the fixing PTF?
If you are at the affected TR level, your workload runs in a pool that uses a pool paging option of *CALC, and you have observed performance issues, you are likely experiencing this problem to some degree and should plan to apply MJ08108 (V7R4) or MJ08141 (V7R5).
How can I determine if my partition is at the affected TR level?
All partitions with TR12 are affected. It is possible the TR was applied if a group PTF was recently applied. It is best to verify using the following CL commands:
V7R4: DSPPTF LICPGM(5770999) SELECT(MJ99312)
V7R5: DSPPTF LICPGM(5770999) SELECT(MJ99407)
Should I apply the fixing PTF if I am not at TR level 12 or 7?
No
Will other Fixes be provided for this issue?
Yes, the problem will be fixed in a two-phased approach. The first fix resolves the performance degradation and a second fix is available now which will provide an enhanced fix to the Disk Meter (which is one of many mechanisms to determine if a pool is under stress). If you have not applied Phase I PTF, you may bypass it and apply Phase II PTF only.
Phase I (DT456038)
7.4 MJ08108
7.5 MJ08141
Phase II (DT456384)
7.4 MJ08158
7.5 MJ08160
Will IBM assess our system and tell us if we are exposed to this issue?
No. If pools are defined with *CALC and the latest TR applied, the defect is in play. The client will need to decide if the performance impact is poor enough to warrant expediting the IPL to apply the fix. The client will need to choose how to limit their exposure by reviewing the proactive steps (listed below) to avoid this problem.
How soon should an IPL be scheduled to apply the fix?
Stable workloads, no performance concerns? You can wait for a convenient IPL window.
Workload expected to increase or performance already impacted? Expedite applying the fix.
What proactive steps can I take to avoid this problem?
IPL and apply the fixing PTF
Role swap to a system that is not affected
Add memory
Tune the SQL statements driving the most asynchronous reads by building supporting indexes (the indexes may reduce the amount of data that needs to be read)
Slip LIC/OS back to TR11 or TR6
Temporarily Disable a setting in SST (*see further notes at the end of this document)
Will changing the paging option to *FIXED resolve the performance problem?
No
Can I remove a PTF to avoid this issue?
No
If I apply the fixing PTF and later decide it needs to be removed, how can I remove the fixing PTF?
If the fixing PTF did not resolve the performance problem, your workload was not affected by the performance issue described in this document. If you need assistance identifying a performance issue, please open a case with the IBM i Global Support Center. In an emergency, if the hiper fix needs to be removed, see https://www.ibm.com/docs/en/i/7.4.0?topic=fixes-removing-software
Will the PTFs be added to the Hiper group PTF?
Yes, the PTFs will be added to Hiper group level 160 (V7R4) and level 88 (V7R5) which will be available on November 25th, 2025.
What should I do if I have more questions?
Open a case with the IBM i Global Support Center. However, as noted previously in this document, the iGSC will not perform an assessment or compare pre/post data. Instead, our support teams will guide you to investigate if a performance problem is happening and which proactive steps are best to implement in your environment.
*NOTES: This macro is being provided as a low-risk, temporary option. The macro will partially emulate the fixing PTF, however, some workloads may only achieve full resolution by applying the PTF. After running the macro, the workload does not need to be restarted. The macro must be manually re-enabled after the PTF is applied.
From the operating system command line, type the following:STRSST (Enter)
Sign in with a service tool profile and password that has authority to Display/Alter/Dump in SST.
Select Option 1 - Start a service tool (Enter).
Select Option 4 - Display/Alter/Dump (Enter).
Option 1 - Display Alter Storage (Enter).
Select Option 2 - Licensed Internal Code (LIC) data (Enter).
Select Option 14 - Advanced analysis (Enter).
Page to the bottom and type 1 next to WRKSQEVAR (Enter).
In the Options field, type m "DbDasdMeterEnableDasdRequestsDepletedCheck" 8 0 (Enter).After the fix is applied, you must revert back to default. To do this, repeat the instructions but change the options field to: m "DbDasdMeterEnableDasdRequestsDepletedCheck" 8 1
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Document Information
Modified date:
10 December 2025
UID
ibm17252010