Re: System slow-down - disk usage?

Absolutely check Richard's suggestion on the Cache Battery. If any of them are dead this sort of performance WILL result during significant I/O.

Going from 60 to 70% DASD should not cause this dramatic slow down. It may cause some small fraction but nothing like 4 times plus.

What is the %BUSY in WRKDSKSTS when the long running job is running? If the disks are 40% or more busy then you likely need more arms, faster arms, or bigger disk cache but even then that's only a 'probable'. Also how many disk arms do you currently have? Are they DPY or MRR protected (From WRKDSKSTS F11)

You also need to check faulting as you mention. The big thing about paging and faulting is the ratios. If the pool running the jobs is paging at say 2500 but faulting at 25 then you're doing exceptionally well as only 1 in 100 pages results in a fault. If you've got 500 faults out of 500 pages then you likely have a memory pool that is far too small or has too many jobs running in it. The reason you don't find specific numbers is because 'It Depends'. If you have a 32 way 595 you can have faulting numbers that would make a 520 user cry and not bat an eye.

What is your system CPW (or processor feature code) and how much memory is installed.

- - DrFranken

On 6/9/2010 6:35 PM, Kurt Anderson wrote:

I'm on v5r4, and we've recently gotten a very large customer and have had some speed issues. At first we thought they were specific to some certain new programs, but today we discovered the issue was impacting another job that was completely an absolutely isolated as far as programs go. So, we were looking at things from a system point of view to see what changed to cause this other job to slow down so much. Our guess - that our % system ASP used went from ~60% to ~70%. Is it possible that that would cause us an issue? (We had a job that would normally run 5 hours take almost 24 hours.)

We IPL'd over the weekend as well. Anyway, I realize this email is probably lacking a lot of specific information, but I'm not really a systems guy, and we're kind of grasping at straws, so I thought I'd see if such a change to disk % used should have such a big impact?

I am looking into other performance improving methods, but at this time we'd really like to pin down the cause of our performance crawl before attempting to put in enhancements.

While I'm at it, I'm curious how to quantify "excessive paging." I've seen reference to that phrase online, yet can't seem to find a number.

Thanks,

Kurt Anderson
Sr. Programmer/Analyst
CustomCall Data Systems