Performance Analysis and Tuning Simplified
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News from Tech Support - The AIX FAQ

SarCheck will find a few bugs in the sar utility, so here's the FAQ section from the manual. These questions make up 80 percent of our support calls.

Frequently asked questions (FAQ):

What am I suddenly getting a message "NOTE: The version number of the agent couldn't be determined"?

Beginning with SarCheck version 7.01.32 for AIX, our agent reports on its version number. We compare the agent's version number with that of the analyze program and report on discrepencies. If you're analyzing old data collected with a pre-7.01.32 version of SarCheck for AIX, you can expect to see this message and it does not indicate a problem. If it did, the message would be preceded with "WARNING" instead of "NOTE".

I just upgraded to AIX 6.1. Why is it warning me about modifications to restricted tunables?

Prior to AIX 6.1 there was no such thing as restricted tunables. Based on information from IBM's formulas and tuning classes, SarCheck made recommendations which were designed to improve your system's performance. If you upgraded to 6.1 and kept the existing tunable values, the operating system will warn you if the values of restricted tunables have been changed. Please check with IBM to see if the non-default values are appropriate to your environment.

When SarCheck wants a restricted tunable changed on AIX 6.1, it will recommend that you check with IBM before implementing the change and it will provide detailed information about why it has recommended the change so that IBM can understand SarCheck's rationale.

What versions of AIX does SarCheck support?

We support AIX 5.2 and up. One binary works with both 32- and 64-bit versions of AIX and it works on every POWER processor that we have tried. It works with physical or virtual systems.

Why doesn't SarCheck tell me about my disks?

SarCheck uses sar to collect data on disk activity and some older versions of sar require an APAR due to trouble with disk stats.

Should I implement recommendations which only show up occasionally?

Feel free to try, but implement the regularly occurring recommendations first, since those will address the most frequently occurring problems. If SarCheck occasionally recommends increasing the amount of memory, you should certainly try it. On systems with some extra memory, SarCheck will be able to make additional recommendations that could not be made on systems where memory is “tight”. Please remember that recommendations (even recommendations made by an expert) should make sense to you before you try them.

Every time I make changes based on SarCheck’s recommendations, it makes more recommendations. Why doesn't it just figure out the correct values for all the parameters?

That’s not how real performance tuning works. There are no “correct” values because tuning is a series of compromises between various system resources. Performance tuning involves a certain degree of trial and error, and gradual change is the only way to do it.

When I try to run sarcheck, I get the message “sarcheck: not found”. What’s wrong?

Check the following:

  • Are you root?
  • Does the sarcheck script really exist? (look for /opt/sarcheck/bin/sarcheck).
  • Is /opt/sarcheck/bin in your PATH variable? (echo $PATH)

Why did SarCheck stop producing reports?

The software has probably expired. Run '/opt/sarcheck/bin/analyze' and look for the expiration date at the bottom of the usage text. If you've licensed SarCheck and the expiration date doesn't make sense to you, run 'analyze -s' and send us the output.

How do I collect data over a 24 hour period?

The adm’s crontab file entries to collect the sar data should look like this:

0 * * * * /usr/lib/sa/sa1 1200 3 &
50 23 * * 1-5 /usr/lib/sa/sa2 -i 1200 -A &

Also, add the entries for root’s crontab entries to collect ps –elf, scaixagent, and fsagent data.

30 12 * * * /opt/sarcheck/bin/fs1 
0,10,20,30,40,50 * * * * /opt/sarcheck/bin/ps1 
55 23 * * * /opt/sarcheck/bin/ps2

How do I collect data every 10 minutes from 08:00 to 18:00?

The adm’s crontab file entries to collect the sar data should look like this:

0 8-17 * * 1-5 /usr/lib/sa/sa1 600 6 &
0 18-7 * * 1-5 /usr/lib/sa/sa1 &

5 18 * * 1-5 /usr/lib/sa/sa2 -s 8:00 -e 18:01 -i 600 -A & 

Also, add the entries for root’s crontab entries to collect ps –elf, scaixagent, and fsagent data.

30 12 * * * /opt/sarcheck/bin/fs1 
0,10,20,30,40,50 8-18 * * 1-5 /opt/sarcheck/bin/ps1 
5 18 * * * /opt/sarcheck/bin/ps2


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