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Memory usage Server 2008 R2 Core with HyperV SP1

    Question

  • Hello,

    I have been struggling with this issue for I while now.

    We have 4 Windows Server 2008 R2 Core servers with HyperV SP1 installed and running in production.
    Each server has 40GB of physical memory available. Virtual memory is configured as following: Automatically manage paging file size for all drives. This means 80GB is allocated as the Virtual Memory size for the HyperV hosts. (I got this data from running Process Explorer on he HyperV hosts).

    The following issue occurs, we monitor a high virtual memory usage on the servers. This is in all 4 cases exactly 50% of the physical memory usage. For example the memory usage of SRVHYP01 is 60%, in this case the virtual memory usage is 30%. For example the memory usage of SRVHYP02 is 82%, in this case the virtual memory usage is 41%.

    Can someone explain to me this high amount of virtual memory usage and why this amount is always 50% of the physical memory usage?

    Thank you all very much for your time.

    Yours truly,


    Mikkie v. Falier

    Tuesday, January 17, 2012 10:49 AM

All replies

  • The pagefile is used for:

    • Supply Virtual Memory to the operating system (i.e. the parent partition). Traditional guidance states ~1.5x the amount of physical memory, although this doesn’t make sense anymore on a >64GB host;
    • Crash dump purposes, but on a hosts with lots of memory (more than 64GB) do you want to have a full memory dump? Look at the number of hours this memory dump will take and you’re convinced that for 98% of all cases a kernel dump is sufficient.

     If you have reserved enough RAM for the host operations and your host is only being used for Hyper-V (plus Fail Over Cluster for HA VMs), you shouldn’t need a large pagefile. Are you using any other application with Hyper-v on the hosts ?

    It is possible to check the pagefile settings using the following command:

    wmic pagefile get /format:list

    Also check

    http://blogs.technet.com/b/rwagg/archive/2010/03/08/how-big-should-pagefile-sys-be-on-a-server-2008-hyper-v-server.aspx

    Here's an old KB article on computing page file size on a large ram machine: http://support.microsoft.com/kb/889654. It explains general principles that are still relevant today. Keep in mind that the counters in the KB article are not relevant for Hyper-V because the standard Windows counters only show you want is going on in the partition you are viewing the counters in. You need to look at Hyper-V counters to know what is happening to the overall physical machine.

    http://social.technet.microsoft.com/wiki/contents/articles/2306.aspx

     http://blogs.technet.com/b/mghazai/archive/2011/05/26/what-s-the-story-of-pagefile-size-on-hyper-v-servers.aspx

     


    Mohamed Fawzi | http://fawzi.wordpress.com
    Tuesday, January 17, 2012 11:55 AM
  • Couldn't agree more with Mr Fawzi.

    Just would like to add this link that was posted by Nicholas Rintalan at Citrix Consulting: http://blogs.citrix.com/2011/12/23/the-pagefile-done-right/

    A long, but very good read when talking about pagefiles.

    Tuesday, January 17, 2012 1:46 PM
  • Thank you Mr Fawzi for your reply, the links you send are giving me a perfect overview about the working process of the pagefile options.

    I executed the following command (wmic pagefile get /format:list) to check ont the page file settings on a HyperV hosts:

    AllocatedBaseSize=40949
    Caption=C:\pagefile.sys
    CurrentUsage=863
    Description=C:\pagefile.sys
    InstallDate=20101216120226.438050+060
    Name=C:\pagefile.sys
    PeakUsage=961
    Status=
    TempPageFile=FALSE

     

    I am a bit concerned about this output because I expected the output to be in next state:

    This is the output Process Explorer gives me. Is there an explanation about the differences in the output of wmic pagefile and process Explorer?

    @Bjorn Andersson: Thank you for your reply, tonight I am going to dive in the article you supplied me with.



    Thank you all very much for your time,

    Yours truly,

    Mikkie v. Falier


    Wednesday, January 18, 2012 7:51 AM