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  • 1.  Host Memory huge, but Guest Memory low

    Posted Apr 16, 2010 09:18 AM

    Hi,

    I'm using an ESXi 4 U1 Hypervisor with one VM on it. It's a Win2k3 VM with applied 4 GB of RAM. The Host Memory it up to 4GB but the Guest Memory is just about 400 MB.

    Why does the Hypervisor not give all that 'unused' memory back to the system?

    Regards



  • 2.  RE: Host Memory huge, but Guest Memory low

    Posted Apr 16, 2010 09:38 AM

    The Host memory will be divided in the VM and the service console.

    Could you check how much memeory is occupied by the service console?

    Jay

    MCSE,VCP 310,VCP 410

    Consider awarding points for "helpful" and/or "correct" answers.



  • 3.  RE: Host Memory huge, but Guest Memory low

    Posted Apr 18, 2010 12:50 PM

    What kind of processors are in the ESXi host? If they are modern processors like an Intel 5500 series (Nehalem) then what you're seeing may be perfectly normal behavior.



  • 4.  RE: Host Memory huge, but Guest Memory low

    Posted Apr 26, 2010 06:35 AM

    Yes it's a new Intel processor. Don't know the exact type right now.

    But why it this a correct behavior? I mean there is just running one guest an it has 4 GB RAM applied and only uses 400MB... So if I want to add additional guest's I can only add one host with 4GB until the RAM is fully used....

    Best regards....



  • 5.  RE: Host Memory huge, but Guest Memory low
    Best Answer

    Posted Apr 26, 2010 01:25 PM

    It is correct behavior because the processor you're using utilizes large memory pages, and the memory sharing feature of ESX (transparent page sharing) can't share those large pages. That means that the VM will occupy host memory equal to what was assigned until you actually exceed the amount of memory in the ESXi. At that point it will automatically break up the large pages into smaller pages and begin sharing memory.

    You can disable the use of large pages with an advanced setting in ESXi called Mem.AllocGuestLargePage. By default it is set to 1, but if you set it to 0 and reboot your virtual machines (reboot of the host isn't required) then they will begin to use small pages instaed. I wouldn't enable this as VMware has seen performance gains from using large pages even if the guest doesn't natively support it.

    Read this thread for more info on this. It sounds like this is exactly what you're describing and again, based on the description above, it is expected behavior.

    http://communities.vmware.com/message/1262016