MustGather: Disk response times and requests

Troubleshooting

Problem

Use this document to collect PEX Trace data for debugging disk IO response times and requests.

Resolving The Problem

Use this document to collect PEX Trace data for debugging disk IO response times and requests.



PEX PDIO traces is used to help analyze disk response times and requests. The trace is obtained using IBM i commands.



Step 1. Verify that the required Performance Explorer (PEX) PTFs are applied

From an IBM i operating system command line, type the following (Note: An IBM Support Representative might change some of the parameters specified, based on a specific problem being reported):



Step 2.

CRTLIB TSXXXXXXX (where XXXXXXX = your Case number) 



Step 3.

QSYS/ADDPEXDFN DFN(PDIO)

TYPE(*TRACE)

JOB((*ALL *ALL))

TASK(*ALL)

MAXSTG(4000000)

INTERVAL(10)

TRCTYPE(*SLTEVT)

SLTEVT(*YES)

MCHINST(*NONE)

BASEVT((*PMCO *NONE *FORMAT2))

DSKEVT((*READEND) (*WRTEND) (*PGREADEND) (*PGWRTEND))

SAREVT((*ALL *NONE *FORMAT2))



Step 4.

STRPEX SSNID(RUN1) DFN(PDIO)



Important Note:  If other PEX sessions are active, this step may fail.



A message CPFAF05 Reason Code 3 would be posted to the joblog of the job that issued the STRPEX command.

RC3 - Definition overlaps with a session that is currently active.



The error occurs only if there is another PEX session running that is also collecting BASEVT(*PMCO) events but is using an INTERVAL size greater than or less than 10 milliseconds. If the CPFAF05 error occurs, you should use ENDPEX (no parameters) and press Enter one time to see if there are other PEX sessions active; then you should wait for this PEX collection to end.



The only way to successfully collect more than one type of PEX trace at a time is to ensure that all of the active PEX definitions (that have BASEVT(*PMCO) specified) are all using the same INTERVAL size.



Step 5. If the desired time period or problem has occurred, stop the trace.

Submit this command to batch using JOBQ qsys/qsysnomax so it runs immediately:

SBMJOB CMD(ENDPEX SSNID(RUN1) DTAOPT(*MGTCOL) MGTCOL(TSXXXXXXX/*SSNID)) JOB(ENDPEX) JOBQ(QSYS/QSYSNOMAX)



Step 6. Once the Batch job in Step 5 completes, save the data to a savf.

CRTSAVF QGPL/PEXSAVF

SAVLIB LIB(TSXXXXXXX) DEV(*SAVF) SAVF(QGPL/PEXSAVF) TGTRLS(*CURRENT) DTACPR(*MEDIUM)



Step 7

. Send the data to IBM.

Instructions for Sending Data to IBM i Support

http://www-01.ibm.com/support/docview.wss?uid=nas8N1019224

The preferred data upload method is QMGTOOLS: FTP Data to IBM

http://www-01.ibm.com/support/docview.wss?uid=nas8N1010370

Step 8. (Optional)



If you would like to analyze the data, consider using IBM's iDoctor PEX Analyzer tool or PRTPEXRPT commands from the operating system command line. To learn more about iDoctor PEX Analyzer, visit

https://public.dhe.ibm.com/services/us/igsc/idoctor/html/pa.html

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Historical Number

663597314

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Document Information

Modified date:
25 July 2023

UID

nas8N1010467

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