ADSM-L

People running OS/390 TSM servers - maybe for the development guys......

2002-03-20 05:54:32
Subject: People running OS/390 TSM servers - maybe for the development guys......
From: Christo Heuer <christoh AT ABSA.CO DOT ZA>
Date: Wed, 20 Mar 2002 12:55:08 +0200
Hi all,

OK - For those of you that does not know anything about
OS/390 or don't run TSM servers on OS/390 this might be
very boring and maybe a bit cryptic - ignore or just
read for the fun.
Now for the people that still run OS/390 TSM servers:

I have always had my doubts about the scalability of
OS/390 when it comes to a TSM server.
Some of you might have seen me posting last year and early
this year about the size of your TSM environment and if
you are happy with the performance of TSM on OS/390 - only
one guy answered giving me specs on the environment they
run(Thanks to William Colwell), but other than that
most people said they moved off OS/390 and are now
running AIX or Sun or even Win2K servers.
William described their environment as an 80 Mips
processor box and a 166Gig db 88% used - and on top
of all that he has good performance from this.

Our environment is a 38 Gig db 80% used and we have
crappy performance. Now in Adsm V3 a new parameter
was introduced called MPTHREADING YES or NO. What
this does is tell TSM that it can start multiple
TCB's on multiple CP's - if you have multiple CP's
on your box.
Now we enabled this and noticed that TSM gets its
knickers in a knot when there are too many things
happening and the system is CPU constrained. In
WLM it is guarenteed to get CPU and in WDM you can
see that about 30% of the time it is delayed for
CPU. What we have done now in Omegamon is to check
how many work each of the TCB's does and then try
and figure out why TSM would perform crappy even though
it is getting about 50% of the total box.
Now - here comes the part where development might
be able to shed some light:

The TCB called dsmserv (the server task), has a
lmod caled IEANUC01 that has a CSECT of IGVGPVT
that uses about 90-95% of all the CPU cycles - remember
that this is one TCB assigned to one CP.
On further investigation our IBM'er came back and said
this IGVGPVT part controls getmain/freemain's for TSM.
Now here comes the question:
How can TSM be using 90% of a CP by just doing getmain/freemain
and all the other TCB's that has a CP allocated just sit
and wait for getmain/freemain's. This looks like a
serious scalability issue with TSM on a multiple
CP environment. According to our performance and MVS
guys the only way we are going to squeeze more juice
out of our OS/390 system with TSM is to split the
workload of TSM and run two TSM servers on one LPAR
or upgrade each CP to a more powerfull CP.
Is this in line with development, and the way it should work?

Thanks
Christo Heuer
ASBA Bank
Johannesburg
SOUTH AFRICA
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