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  • VMWare Server memory usage

    Hi, guys.
    I have an older server, Dual Xeon 2.4GHz, 2GB RAM. For backup purposes, I want to install on it VMWare Server and move to it some of my servers, that are mission-critical. I am talking about 2 or 3 such servers. The amount of memory these servers have today on the physical machines is 4GB.
    I know I can give a virtual machine a specific amount of memory and VMWare will allocate as much as it needs.
    The question is: let's say I am in deep s**t and all my physical machines are gone and I have to turn on the virtual ones. Will I be able to run all of them? Does VMWare Server know to split the physical resources between the machines it has to run? What will happen if there's suddenly need of more memory? Will the machines collapse?

    Thank you in advance for your answers. I hope I didn't make too much fool of myself, the virtual universe is new to me (hope that no for long ).

    Sorin Solomon


    In order to succeed, your desire for success should be greater than your fear of failure.
    -

  • #2
    Re: VMWare Server memory usage

    Hi Sorinso,

    Thanks for your post.

    These are good questions!

    Do you think that you would ever loose all the primary machines and have to bring up all the backup machines - such as with a disaster scenario (assuming the vmware backup machine is located offsite)? If so, then you certainly need to ensure that the virtual server could run all the machines it may be loaded with, if a disaster occurred.

    How much RAM do you think that the current physical machines really need for production or could get by with without a noticable decrease in performance to the end users?

    Will I be able to run all of them? Does VMWare Server know to split the physical resources between the machines it has to run? What will happen if there's suddenly need of more memory? Will the machines collapse?
    Say you did have to turn on all of them, with the default settings, you wouldn't be able to allocate more RAM to all STARTED guest VM's than the physical amount of RAM plus some swap. And I wouldn't recommend changing that setting. I attached a screenshot of the window I am talking about.

    Yes, VMware will share the RAM & swap resources between all the running virtual machines without any trouble. You just want to make sure that you have enough RAM to allocate the minimum amount of RAM needed to still be able to run the production servers.

    For example, say you have 3 physical servers with 4GB each. On the backup system (vmware host) you have 2GB of RAM, perhaps you could allocate 512MB to each guest VM. That would take up 1.5GB, leaving 512MB for the host OS. Would the end users be seriously hampered by having only 512MB of RAM on these machines? You could increase that by using swap to, say, 768MB per system but I'm not sure you could go too far beyond that. You don't want to end up with 3 systems with 1GB of RAM each but it is really all just swap. Those would be some poorly running systems.

    I hope I helped out.

    Anyone else want have any suggestions for Sorinso?
    Attached Files
    David Davis - Petri Forums Moderator & Video Training Author
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    • #3
      Re: VMWare Server memory usage

      Hi, David.
      Thank you for your response. I really hope that I will never be in the situation that all those machines will go down together.
      I tried in my question to understand better the mechanism in which VMWare deals with the memory allocation.
      Virtualization does have its advantages, but needs the right resources for them

      Sorin Solomon


      In order to succeed, your desire for success should be greater than your fear of failure.
      -

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