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 [EMAIL PROTECTED] Nyherji Hf Simi TEL: +354-569-7700 Borgartun 37 105 Iceland URL: http://www.nyherji.is -----Original Message----- From: ADSM: Dist Stor Manager [mailto:[EMAIL PROTECTED]]On Behalf Of Seay, Paul Sent: 16. september 2002 22:00 To: [EMAIL PROTECTED] 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