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How many available vCPU's would I have....

    Frage

  • Ok, I've read lots about vCPU's and how many per core, per physical socket, etc., and I just want to clear this up before I pull the trigger on a purchase.  I'm planning a new Hyper-V server running on dual Xeon X5690 processors.  Each processor has 6-cores, 12 threads and runs @3.46GHz.  So, my math from what I've read says I will have a safe minimum of 96 vCPU's available for whatever mix of guests I choose.  (2CPUs * 6cores * 8ratio)  Is this correct?  Does HyperThreading add to the number of vCPU's that would be available?  How about the 12 threads that each CPU runs?  In addition, each CPU will have 72GB of RAM, for a total of 144GB per server.  Will Windows 2008R2/Hyper-V see all 144GB of RAM and make that available to the mix of guests?  Thanks!

    Mittwoch, 2. Mai 2012 16:16

Antworten

  • never include hyperthreading in vCPU counts.  All you should concern youself with is cores and threads (technically).

    The conservative estimate is 1 core has 8 threads.  Therefore 1 core gives 8 vCPU.  (becuase that was the common number when most guidance was written).

    If you know the thread cound of your system is higher, then you get more vCPU.  Lower and you get less.  Some processors report the threads as Logical Processors.  It is the same, logical processor threads...

    Each VM gets a slice of a physical RAM - don't think RAM per Core as you do when running an applicatoin server on bare metal - this works totally different - all resources are subdivided.


    Brian Ehlert
    http://ITProctology.blogspot.com
    Learn. Apply. Repeat.
    Disclaimer: Attempting change is of your own free will.

    Mittwoch, 2. Mai 2012 16:56
  • Hi!

    Please note that I'm not a Microsoft representative.

    According to the Microsoft virtualization product team blog post here: http://blogs.technet.com/b/virtualization/archive/2011/04/25/hyper-v-vm-density-vp-lp-ratio-cores-and-threads.aspx

    There is an implication that you might take hyperthreading into count when calculating your expected limit of vCPU consumption, but there are plenty of articles and experts that says that you shouldn't. I personally haven't gone deep on that one.

    There is no upper limit on how many vCPU's you are allowed to assign to virtual machines. There is of course a technical limit somewhere, but that is a Hyper-V boundary and totally irrelevant to what kind of equipment you have.

    Just keep in mind that in common virtualization scenarios, CPU is rarely the bottleneck. The 2*6*8 equation is a rule of thumb more than anything and it really comes down to what kind of virtual machines your runing and what kind of workload the hold. A combination of performance monitoring and common sense will get you very far in vCPU planning.

    Mittwoch, 2. Mai 2012 16:39

Alle Antworten

  • Hi!

    Please note that I'm not a Microsoft representative.

    According to the Microsoft virtualization product team blog post here: http://blogs.technet.com/b/virtualization/archive/2011/04/25/hyper-v-vm-density-vp-lp-ratio-cores-and-threads.aspx

    There is an implication that you might take hyperthreading into count when calculating your expected limit of vCPU consumption, but there are plenty of articles and experts that says that you shouldn't. I personally haven't gone deep on that one.

    There is no upper limit on how many vCPU's you are allowed to assign to virtual machines. There is of course a technical limit somewhere, but that is a Hyper-V boundary and totally irrelevant to what kind of equipment you have.

    Just keep in mind that in common virtualization scenarios, CPU is rarely the bottleneck. The 2*6*8 equation is a rule of thumb more than anything and it really comes down to what kind of virtual machines your runing and what kind of workload the hold. A combination of performance monitoring and common sense will get you very far in vCPU planning.

    Mittwoch, 2. Mai 2012 16:39
  • More like 4 VCpu for 1.

    But its recommend, you can always go ahead with more and see if that works for you. Do tests as always.

    See this on 17:54 to 18:25

    http://channel9.msdn.com/Events/TechEd/NewZealand/2010/SVR313

    And also, they give you a code for Powershell to asset your ratio. That could help you.

    About Hyper threading, it depends.

    The old version of Hyper threading is bad (the first version released by Intel), and the new Hyper threading is good.

    You can enable it, however, do not count them as they will double your CPU proccesors.

    See from 29:46 to 32:05

    For memory, remember to leave at least 1 Gb available to the host.

    Mittwoch, 2. Mai 2012 16:47
  • never include hyperthreading in vCPU counts.  All you should concern youself with is cores and threads (technically).

    The conservative estimate is 1 core has 8 threads.  Therefore 1 core gives 8 vCPU.  (becuase that was the common number when most guidance was written).

    If you know the thread cound of your system is higher, then you get more vCPU.  Lower and you get less.  Some processors report the threads as Logical Processors.  It is the same, logical processor threads...

    Each VM gets a slice of a physical RAM - don't think RAM per Core as you do when running an applicatoin server on bare metal - this works totally different - all resources are subdivided.


    Brian Ehlert
    http://ITProctology.blogspot.com
    Learn. Apply. Repeat.
    Disclaimer: Attempting change is of your own free will.

    Mittwoch, 2. Mai 2012 16:56
  • while its unlikely that you use standard edition on this machine config, keep in mind that it would have a memory limit of 32gb (http://msdn.microsoft.com/en-us/library/windows/desktop/aa366778(v=vs.85).aspx#physical_memory_limits_windows_server_2008_r2)
    Mittwoch, 2. Mai 2012 17:00
  • I saw that link before and I see they list 8:1 as the supported ratio for vCPU to logical CPU.  Either way, 4:1 or 8:1, I will still almost double my current ESX hosts that we are migrating from.  I have two hosts, and each host has approx 25 vCPU's in use on much smaller hardware.  I know it's not exactly an apples to apples comparison (ESX to Hyper-V), but I'm pretty confident that it's close enough that CPU resources won't be my bottleneck in the future just as it isn't now. 

    Sorry, wrong link I was referring to.  Here is the link I mentioned, not yours.

    http://technet.microsoft.com/en-us/library/ee405267%28WS.10%29.aspx

    • Bearbeitet BClark22 Mittwoch, 2. Mai 2012 18:31
    Mittwoch, 2. Mai 2012 18:18
  • You are correct, I'm looking at Enterprise or Datacenter, depending on the licensing model.  I will have for starters 12 server guests on each Hyper-V host, only going to go up from there.  I remember somewhere reading the "break-even" point in regards to licensing on Enterprise or Datacenter versions, just need to find it again and do some calculations.

    Mittwoch, 2. Mai 2012 18:21
  • CPU is very rarely a bottleneck unless you get into a situation where you are over-subscribed.  Which can be done on any hypervisor.

    The 8 vCPU to 1 physical core is a very (highly) conservative number. 

    (MSFT used to talk logical cores but has since stopped as it is too confusing as the hardware vendors don't all report it ithe same and it is not equal processing).


    Brian Ehlert
    http://ITProctology.blogspot.com
    Learn. Apply. Repeat.
    Disclaimer: Attempting change is of your own free will.

    Mittwoch, 2. Mai 2012 20:10