ADSM-L

Re: Optimal VMTUNE Guidelines for a TSM Server

2002-09-17 08:29:43
Subject: Re: Optimal VMTUNE Guidelines for a TSM Server
From: Pétur Eyþórsson <peddi AT ITN DOT IS>
To: ADSM-L AT VM.MARIST DOT EDU
Date: Tue, 17 Sep 2002 12:22:54 -0000
Hey Seay,

here are a few hints on vmtune.

Provided in the bos.adt.samples fileset
found in /usr/samples/kernel (not in default path)
Contorles varius aspects of the AIX virutal memory system. The virtual
memory system contorls most filesystem activity on AIX.
Changes to vmtune parameters do not surive reboot. But A line can be added
to /etc/inittab so that vmtune settings are set upon reboot.
If AIX detects that file reading is happening sequentially it can read ahead
even though the application has not (yet) requested that data.

Helps large file backup on AIX clients and helps storage pool migrations
from disk on an AIX TSM server. When altering the read ahead parameter (-R)
you must also alter the maxfree parameter (-F) so that there is enough free
memory to store the read ahead data. The following equation MUST HOLD:
minfree + maxpgahead <= maxfree
I reccomend the maximum: -R256

If you look at vmtune - minperm/maxperm
it detemens how mutch memory AIX sets aside for file system cache. AIX
can/will throw out application like TSM memory in favor of caching
filesystem data. This can cause paging of the database buffer pool leading
to slow database perfomance. Paging of the database buffer pool can cause
database cahce hit statisitics to ber overly ooptimistic. TSM dos not often
take adcantage of any filesystem caching. So i recomend you to lowvering the
maxperm will make AIX retain more application memmory. Most VM paging on a
TSM (only) server can be stopped by modifying the minperm/maxperm
parameters.
Exeption: RAM constrained systems and database buffer pool size is to large.
Good starting poing is setting aside a max of 50% (-P50) for filesystem
caching instead of the default of 80%.
Lower further if no effective, this changes can be done on the fly. As
maxperm approaches minperm, consider lowering minperm as well and watch
vmstat for progress, if po´s go to zero pi´s will eventually lower as well.


Ok i know of 2 good books that cover this concepts.

Please read this readbook

IBM Certifacation Study Guide AIX Perfomance and System Tuning.

and this book, (this is not a redbook and you need to buy it)

AIX Perfomance Tuning, by Frank Waters.


Hope this helps you Paul

Pete out :-)


Kvedja/Regards
Petur Eythorsson
Taeknimadur/Technician
IBM Certified Specialist - AIX
Tivoli Storage Manager Certified Professional
Microsoft Certified System Engineer

peddi AT itn DOT is

 Nyherji Hf              Simi TEL: +354-569-7700
 Borgartun 37            105 Iceland
 URL:                    http://www.nyherji.is


-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU]On Behalf Of
Seay, Paul
Sent: 16. september 2002 22:00
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Optimal VMTUNE Guidelines for a TSM Server


I am trying to figure out what these are.  The defaults are not good on a
large server.

The suggestion is figure out how much memory does dsmserv need and then work
from there.

So lets take the example of a 2G server with a buffer pool of 256MB and an
overall memory requirement of 400MB.  That would make you think there is
about 1.6GB left around.  Problem is the default filesystem maxperm is 80%
of the 2GB or about 1.6GB.  This would mean nothing left for the rest of the
processes, thus lots of paging.  I am thinking a buffer of about 128MB
should be in there.  So, in this case, maybe set maxperm to 65%.

The real question is what other vmtune knobs should be considered in a TSM
server.  The IO prefetch, large or small?  Is there a book on how to do
this?

ETC
ETC.

Paul D. Seay, Jr.
Technical Specialist
Naptheon Inc.
757-688-8180