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How is this possible? 4 virtual CPUs in Server 2003 Guest

    Question

  • I used SCVMM to import a machine previously with 4 processors, into Server 2008 R2 Hyper-V.   I was in a hurry and neglected to reduce the setting in SCVMM Import from 4 to 2 CPUs.  So the machine was converted and configured with 4 CPUs.

    Problem is, the guest is running Server 2003 SP2 and Task Manager shows all 4 CPUs.

    How is that possible?  It thought Server 2003 guests were limited to 2 CPUs?

    Sunday, December 4, 2011 12:55 AM

Answers

  • There is no forced limit, you can use more than 2.  The "limit" is what is tested and supported by Microsoft. 
    Sunday, December 4, 2011 1:55 AM
  • Hi Rebus9,

    Did you know that in Hyper-V we are limited to 4 CPU per virtual Machine ?

    And did you that with a simple configuration file modification, we can set 5, 6, 7, 8 or more CPU to one virtual machine ?

    SO the problem is not, how much CPU can i give to my VM but is Microsoft supporting me or not ?

    So if you neglect the Microsoft support you can put 4 CPUs for your Windows Server 2003 VM. It will maybe functions normally all its existence, but if any issue is happening for your 2003 VM (even inside, disk corrupted) Microsoft will not support you and if the problem is huge, you will have to face it alone.

    So in the supported guest OS list, Microsoft mentions that only 2 virtual processors are supported for Windows Server 2003


    Regards, Samir Farhat Infrastructure Consultant
    Sunday, December 4, 2011 11:55 AM

All replies

  • There is no forced limit, you can use more than 2.  The "limit" is what is tested and supported by Microsoft. 
    Sunday, December 4, 2011 1:55 AM
  • Is there performance degredation when using 4 versus 2 processors in a Server 2003 guest? 

    I don't want to make the physical CPUs busier, when the benefits are going to be minimal due to some limitation in the hypervisor's ability to support that many in 2003. 

    Or is the "offically supported" limit of 2 CPUs just a marketing ploy to get us to upgrade to 2008 if we want to use 4 CPUs in a VM?


    • Edited by rebus9 Sunday, December 4, 2011 3:12 AM
    Sunday, December 4, 2011 3:11 AM
  • Hi Rebus9,

    Did you know that in Hyper-V we are limited to 4 CPU per virtual Machine ?

    And did you that with a simple configuration file modification, we can set 5, 6, 7, 8 or more CPU to one virtual machine ?

    SO the problem is not, how much CPU can i give to my VM but is Microsoft supporting me or not ?

    So if you neglect the Microsoft support you can put 4 CPUs for your Windows Server 2003 VM. It will maybe functions normally all its existence, but if any issue is happening for your 2003 VM (even inside, disk corrupted) Microsoft will not support you and if the problem is huge, you will have to face it alone.

    So in the supported guest OS list, Microsoft mentions that only 2 virtual processors are supported for Windows Server 2003


    Regards, Samir Farhat Infrastructure Consultant
    Sunday, December 4, 2011 11:55 AM
  •  So in the supported guest OS list, Microsoft mentions that only 2 virtual processors are supported for Windows Server 2003


    Right, which is why I opened this thread.  When converting the machine with SCVMM, by mistake I did not reduce the CPU selection from 4 to 2.  I never intended to give more than 2 CPUs to a 2003 guest.  I could not understand how all 4 CPUs were recognized by the VM.

    I read "only 2 virtual processors supported for a Server 2003 guest" and interpreted that as "it is impossible to use more than 2".  I didn't know that it was "possible, but Microsoft won't help you if there are problems".

     


    • Edited by rebus9 Sunday, December 4, 2011 1:05 PM
    Sunday, December 4, 2011 1:04 PM
  • Hi!

     "possible, but Microsoft won't help you if there are problems", not really true.

    If you encounter problems then Microsoft will recommend you to reduce the number of virtual CPU's down to 2 as a first course of action, if that resolves the issue, no further troubleshooting steps will be taken.

    Sunday, December 4, 2011 1:34 PM
  • The system runs in a medical (clinical in-patient) environment, so even 5-10 minutes downtime to shut down the machine, remove CPUs and reboot, is going to create mild chaos.

    Realistically, what kinds of problems are people seeing with "too many" CPUs in a 2003 guest?   If the system is at moderate (or higher) risk of corruption, then we'll have to do it.  Otherwise, I'd like to postpone until the next scheduled maintenance window if the risk is minimal.

     

     



    • Edited by rebus9 Sunday, December 4, 2011 3:37 PM
    Sunday, December 4, 2011 3:36 PM
  • Hi,

     

    As the above guys mentioned, 2 virtual processors for Windows Server 2003 virtual machines is tested and supported by Microsoft. You can use more than 2 virtual processors on a Windows Server 2003 virtual machine.

     

    In this forum, I have seen some perform issue with virtual machines which had inappropriate number of virtual processors, when they reduce the number of virtual processor, the issue disappeared. You can try to keep 4 virtual processors with the virtual machines if there is no time to power off the virtual machine.

     

     

    Best regards,

    Vincent Hu

     

     

    Monday, December 5, 2011 3:15 AM
    Moderator
  • There can be problems, just recently there was a similar thread discussing this and that one poster had strange issues with 4 vCPUS in 2003.
    Here's the thread: http://social.technet.microsoft.com/Forums/en-US/winserverhyperv/thread/d0e019f2-382f-4daa-9494-4a158ebe301d

     

    • Edited by essjae Monday, December 5, 2011 3:29 AM added link
    Monday, December 5, 2011 3:27 AM