Windows and AIX platforms need more memory so they can buffer data in memory and avoid I/O. In general, zLinux images should be trimmed smalle r to avoid buffering large amounts of data in guest memory and instead use
MDCACHE in XSTORE memory to avoid the I/O. I'd call it an Apples to Oranges comparison without having lots more details. We don't run WAS or Websphere, so I can't comment on if they are exceptions to the general zLinux size trimming or not. Brian Nielsen On Thu, 13 Aug 2009 16:03:33 -0400, Dean, David (I/S) <david_d...@bcbst.com> wrote: >Thank you, the problem however is exactly what you allude to, what size do they REALLY need to be. IBM is comparing WebSphere RAM needs between AIX, Windows, and zLinux. We have historical data that help us compare AIX needs to Windows needs, but no one is able to help us determine how that compares in zLinux land. Subsequently when an app comes along that specifies 8G in AIX or Windows people are making the leap to say that we will need 8G on zLinux...which is ludicrous...it is an apples to oranges comparison. Are there any studies, metrics, stats, whatever that anyone has that could help? Also, for this project I am referring to a heavy WebSphere / Java environment. > > >David Dean >Information Systems >*bcbstauthorized* > >-----Original Message----- >From: The IBM z/VM Operating System [mailto:ib...@listserv.uark.edu] On Behalf Of Marcy Cortes >Sent: Thursday, August 13, 2009 3:31 PM >To: IBMVM@LISTSERV.UARK.EDU >Subject: Re: Virtual vs. Physical Memory in ZVM > >David, > >I don't think anything stated below is wrong. > >I would question whether you really need those guests to be 6G. Our WAS 6.1 guests range from 1G-8G, with the majority of them in between 1G and 2G. > >The overcommittment ratio you tolerate depends heavily on the robustness of your paging subsystem. It also depends on how idle/not idle they are. > >At one point we had about 100 servers, about 1/2 of them WAS on 24G of real, overcommitt of maybe 5:1. That was painful (and amazing that VM ca n page in the 10's of thousands per second). >But it was test/dev. We wouldn't do that to production. > >At the moment, I'm looking at one test system that is 2.1:1 on 44G with 38 servers up on it. It is paging only a couple of hundred per second on average and hasn't gone higher than about 2500/sec today. No one is complaining. That one can probably go to 2.5:1 with no issues. > > > >Marcy > >"This message may contain confidential and/or privileged information. If you are not the addressee or authorized to receive this for the addressee , you must not use, copy, disclose, or take any action based on this messag e or any information herein. If you have received this message in error, please advise the sender immediately by reply e-mail and delete this message. Thank you for your cooperation." > > > >________________________________ > >From: The IBM z/VM Operating System [mailto:ib...@listserv.uark.edu] On Behalf Of Dean, David (I/S) >Sent: Thursday, August 13, 2009 7:47 AM >To: IBMVM@LISTSERV.UARK.EDU >Subject: [IBMVM] Virtual vs. Physical Memory in ZVM > > > >HELP! > > > >Warning -the below is from an IBM rep, the name removed to protect the innocent(?). This is a portion of the analysis comparing real (physical) memory needs for zLinux guests versus AIX. The 2:1 ratio used below (in my humble opinion) is extreme overkill. I need the experts (you) to comment. > > > > > > > >The main disclaimer is that we have no way to determine whether the virtual memory requirements (which are used to calculate the real memory) would be significantly less on System z. In most cases they are. For example, 6GB is a pretty large Linux guest memory size for a WAS guest unless they are running super large Application HEAP spaces and / or are running multiple JVM's in each Linux guest. > >Nonetheless if we use a 2:1 Virtual to Real memory Ratio then we simply take all the guests add them up divide by 2 for the required real Central Storage, add in about 500 MB for VM and 2 GB for Expanded Storage. > >5 - Linux Guests with DB2 at 6 GB Virtual = 30 GB Virtual >20 - Linux Guests with WAS at 6 GB Virtual = 120 GB Virtual >------------------------------------------------------------------------ -- --------------- >150 GB Virtual / 2 = 75 GB Real + 500 MB Real + 2GB Real = 78GB Real > > > > > > > >David Dean > >Information Systems > >*bcbstauthorized* > > > >----------------------------------------------------- >Please see the following link for the BlueCross BlueShield of Tennessee E- mail disclaimer: http://www.bcbst.com/email_disclaimer.shtm > >----------------------------------------------------- >Please see the following link for the BlueCross BlueShield of Tennessee E- mail disclaimer: http://www.bcbst.com/email_disclaimer.shtm >======================== ========================= =======================
