Did you also try with -c Flag too along with -P and -p Flag!!!topas will
show its effect too.

-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of
Peter Jones
Sent: Tuesday, September 21, 2004 10:52 AM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Re: AIX/TSM Paging Space and Memory Settings


Hi,

Since nobody else went in for the big explanation I thought I might.


AIX memory tuning can help TSM performance significantly. We run on RAW
LVs and set the AIX box to not page at all.

>From our experience, the key seems to be the paging of the bufferpool.
TSM keeps this cache of DB pages in memory to speed things up, if they
end up put back on disk (usually slower system disks) then the advantage
is lost, even if the cache hit% is high, the performance will be low as
the system disk and the paging space on it becomes the bottleneck.

My understanding is that AIX memory gets divded up into two types:
computational (application code/storage) and non-computational/file
(basically jfs file caching). The minperm/maxperm settings determine
which of these gets paged out when AIX gets short on memory. When
computational pages get paged out they go to the paging space, when
non-computational pages get paged out they go back to their backing disk
storage, where they came from.

To stop the system paging out the TSM bufferpool, we found the right
balance for our systems. This involved working out how much various
applications used and setting the minperm/maxperm to match.

For example, a theoretical system with 2GB may use memory in the
following way:

512MB  - AIX + local apps (about right on our hosts)
512MB  - TSM bufferpool
512MB  - TSM code etc

???MB  - AIX file caching

The aim would then be to tune the system so that it always had at least
1.5GB of computational memory available. That way TSM should never get
paged out. To do this on this system would require setting the
maxperm/minperm combination to something like 20/10, meaning 80% (5%
"breathing" space) of memory should remain computational (AIX, TSM, the
TSM bufferpool etc) and a max of 20% for AIX's file caching. With these
settings when AIX gets a little short on memory it should eat into the
file cache and not the TSM bufferpool.

If you don't use RAW LVs for your LOG/DB/DISK STGPOOLS then you have an
added factor to think about. The JFS file caching (non-computational)
may actually be helping you, it is another layer of caching being
utilised before the data hits the physical media. Careful consideration
needs to be given to how much room to give to this (especially if it
helps with STGPOOL which doesn't get its own bufferpool).


For better explanations and a better overview on AIX performance:

AIX 5L Performance Tools Handbook

http://www.redbooks.ibm.com/abstracts/sg246039.html



Sorry for the long post,

Pete

--
Peter Jones
Unix Systems Programmer (HFS)
Oxford University Computing Services