Dynamic Memory allocation in Hyper-V R2 RRS feed

  • Question

  • Hi all,

    I understand that Hyper-V R2 is missing the dynamic memory allocation feature?
    Could someone 'in the know' elaborate on why this wasnt included...and maybe tell me if it will be arriving soon?

    many thanks.

    Thursday, August 20, 2009 10:55 AM


All replies

  • This is one of those mixed-bag types of features.

    First of all, the OS has to support it and off the top of my head - I cannot think of an OS that can handle a memory change while it is running (reboot required).  Please tell me if I am wrong, as I will want to try that.

    Therefore, I am guessing that it fell lower on the list of priorities (Live Migration being at the top).

    I know of one hypervisor that allows the memory setting to be changed while the VM is running, however the change is actually applied when the vm is rebooted.  Thus giving the OS a change to deal with the change.

    Brian Ehlert (hopefully you have found this useful)
    Thursday, August 20, 2009 3:02 PM
  • VMWare supports memory overcommit with a special driver. Not recommended for production use, for security and performance reasons (or so I've heard).  

    Thursday, August 20, 2009 5:04 PM
  • Overcommitment is a totally different feature than modifying the RAM setting of a running virtual machine.

    If that is what Gav_pop is referring to (I appoligize for not fully understanding) that is also not a feature that made it into R2.

    Overcommitment fits the VMware model and architecture, and does not really fit the current architecture of Hyper-V.

    That being said - there are many ideas to handle "overcommitment" or "dynamic allocation"

    They all support the basic idea of the virtual machines on the host actually having the potential to use more RAM than the Host physically has.

    And yes, as Ascendo points out, this is no longer recommended for Production (the assumption is that Production wants the best possible performance and security).
    Again, the IT axiom - "just because you can, should you?"

    Brian Ehlert (hopefully you have found this useful)
    Thursday, August 20, 2009 5:10 PM
  • ·         Hi,


    I want to see if the information provided was helpful. Your feedback is very useful for the further research. Please feel free to let me know if you have addition questions.



    Best regards,

    Vincent Hu

    Monday, August 24, 2009 2:59 AM
  • Overcommitment is not what I am referring to.

    Dynamic Memory Allocation would have been extremely useful in my organisation.
    Reasons -
    I am an IT manager for a software development business.
    Hyper-V has been a boon for us, for the fact that the developers can now have a multitude of OS's and a very broad range of software installed on these OS's.
    With Hyper-V we have gone from 8 servers to over 80.
    One problem though is getting the developers to appreciate the resources they use when they turn a VM on, but then dont turn it off when they've finished.   This hogs resources and slows things down.
    Dynamic Memory Allocation would have helped by reducing the RAM on these unused(but switched on) VMs and giving the RAM to the used VMs.
    Obviously I could do an automated shut-down each evening, but I really only want to do this as a last resort.

    Its a shame Dynamic Memory Allocation didnt make it into R2.

    Monday, August 24, 2009 9:41 AM
  • Hi,


    Currently, I am sorry to let you know that Dynamic memory allocation is not possible in Hyper-V.


    The following post discussed the similar issue, you can refer to:


    Dynamic memory allocation across virtual machines


    By the way, as Microsoft continues to collect product feedback from the Connect web site, we appreciate your efforts in submitting your feedback via the following channels to help us improve our products.


    Windows Server 2008 Feedback Home



    Best Regards,

    Vincent Hu


    Monday, August 24, 2009 10:21 AM
  • Hello Buddy,


    Good news and your questions are answered here .


    check the issue



    Hope that helps


    Rajesh Parasa

    Tuesday, April 13, 2010 8:33 AM
  • hi Gav

    maybe this will help , Dynamic memory is now avaliable on SP1 for windows server 2008 R2 along with remote Fx enhancements

    SP1 is still in beta anyway ,

    Tuesday, July 27, 2010 10:01 AM
  • Please see the following blog post and the new feature realesed in SP1.

    Dynamic Memory is a beta feature which will be included in Windows server 2008 R2 SP1.

    This is an answer update which should be marked as the current correct answer.

    • Proposed as answer by Jeff Loucks Sunday, August 29, 2010 2:13 PM
    Sunday, August 29, 2010 2:12 PM