How many processors can I assign to a virtual guest in Microsoft Hyper-V Server 2008 R2

Posted on 2010-01-05
Last Modified: 2013-12-10
I am trying to get a definitive answer on how many processors I can assign to a virtual guest in Hyper-V Server 2008 R2.  I have read where Hyper-V will support up to 64 logical processors on the host box.  Does anyone have any insight into this for the guests?

Question by:Netopsprime
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    Expert Comment

    This article may help you, not sure about max. processor per guest VM , i can find that out for you. i am more into VMware than Hyper V.'

    If you have ever experimented with the various settings in Hyper-V, then you probably know that Hyper-V offers a lot of flexibility when it comes to allocating CPU resources to virtual machines. In a way this is both good and bad. It is good, because Hyper-V allows you to achieve granular control over the allocation of system resources. The bad part is that it is possible to allocate CPU resources in a way that starves the server of processing power.
    Virtual Processor Mapping
    One of the reasons why there is so much flexibility in allocating CPU resources is that every version of Windows that has been built on the Windows NT kernel (or some variation of it) supports at least two processors. Every computer being manufactured today includes multiple CPU cores, and in many cases multiple CPUs, each of which contain multiple CPU cores.
    What this means is that you have a lot of flexibility in deciding how many CPU cores you want to allocate to each guest operating system. If you look at Figure A, you can see that Hyper-V allows you to decide how many virtual processors you want to assign to a guest operating system. Before you start doing that though, you need to understand that when you assign CPU resources to a virtual machine, you're not assigning physical CPU cores but rather virtual processors.
    Hyper-V allows you to decide how many virtual processors you want to assign to a guest operating system.
    A virtual processor does not necessarily have to correspond to a physical processor or to a physical CPU core. Microsoft recommends that you maintain a one-to-one ratio of virtual processors to physical CPU cores. On top of that, I recommend that you reserve at least one CPU core for the host operating system. This means that if you stick to the recommendation, a server with four CPU cores could host up to three virtual machines, with one virtual processor each (because one cores being used by the host operating system). You can also host two virtual machines, one with two virtual processors in one with one virtual processor.
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    Expert Comment

    4 Processors max...

    I went ahead and tested it to be sure on both Hyper-V console and VMM using 32 bit and 64 bit OS's inclding 2008 R2. the max was 4 processors.


    Author Comment

    Follow-up question - based on your response (max 4 processors)  does that mean if I have 4 processors - 4 cores each for a total of 16 cores - that i could assign 8 or 10 or 12 or 15 cores to a single VM?
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    Expert Comment

    Nope. 4 logical cores per VM.

    My test was done on dual Quad core Intel x5550 nahelam procs with Hyperthreading (16 cores presented to the host total). Still only 4 processors per VM...
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    Accepted Solution

    4 on the guest.
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    Expert Comment

    Forgot the link. Scroll to the bottom.

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