SMS Trace

vasanthz · Posted: Tue Apr 16, 2013 6:56 pm

Hello,

Could you please let me know how SMS trace is useful. An example scenario would be very helpful.

searching the web shows "SMS provides a trace table for you to use when working with the IBM® Support Center on a problem. The IBM Support Center may request a copy of the SMS trace table. "

I can see that SMS trace is ON in some LPARS and OFF by default in some LPARS. Is there any rule of the thumb when the trace has to be ON or OFF.

Thanks & Regards,

vasanthz · Posted: Wed Apr 17, 2013 3:36 pm

Hello,
One more query.
Could you please let me know if it is possible to find out how much CPU SMS trace alone is using. As far I searched, I was unable to find trace related fields on SMF. But there is high probability that I did not look in the right places.

Thanks & Regards,

enrico-sorichetti · Posted: Wed Apr 17, 2013 3:39 pm

since most of the SMS activity takes place at allocation time
I would say that the overall impact might be negligible.

Pete Wilson · Posted: Thu May 16, 2013 1:07 pm

The trace can be activated for just selected events. The D SMS,TRACE command shows which ones are active.

I have worked at many different places and some have all traces on and some have all off, and some have only selected events active. I'm not sure if there's any rule of thumb you can apply, but at least if they are active you may have more chance of finding something useful in any related dumps the system takes which might enable IBM to provide help more quickly.

It's hard to find much information about the overhead of SMS in general, although when I first started using it about 1989 there was talk of a 17% overhead at that time which seemed alot. Not sure if that has changed. I'm not sure what effect tracing has on that bottom line figure, but tuning your ACS routines can have some effect, for example having the most commonly occuring variables specified at the start of filtlists, keeping filtlist to a minimum.

vasanthz · Posted: Fri May 17, 2013 4:28 pm

Hi Pete, Thank you for your perspective.

As far as I have searched the interwebs, there are no documented formats to read trace output data and I believe it is intended to be used only by IBM and not by users. Some internet links mentioned that Traces can be set to off at all times and can be turned on only when required, So I am nudging my sysprogs to turn it off in test systems and see the impact.

Pete Wilson · Posted: Fri May 17, 2013 5:23 pm

Sory Vasanth, I can't remember what that 17% related to. I guess it increases the code path length for any dataset allocation and the storgrp monitoring etc, but I have no idea how you'd measure it.

I don't think it is worth pursuing as what are you going to do, take out SMS?

vasanthz · Posted: Fri May 17, 2013 5:31 pm

Pete, Only planning to switch off SMS tracing