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  • Logical Processor?

    Hi Everyone,
    A pleasant day to you all!

    I am pretty new at VMware server.

    I want to install VM in HP Proliant DL 360 G6
    Hyperthreading : Enabled.
    CPU: x5550 (quad core x 2 socket)
    OS: Windows server 2003 / 2008 x64

    according to hardware spec, it supposed to be 8 logical CPU..but vmware says that Logical Processor : 16

    Based on my research, because of Hyperthreading...

    What the total amount of CPU can i assign to the vm?

    8 or 16?

    if only 8 is avail, I want to install 3 vms in esxi server as follows

    1. CPU : 4
    2. cpu: 2
    3. cpu: 1

    total is 7 , 1 for hardware.

    I think i need to remain at least 1 logical cpu for hardware uses.

    it 16 is avail, i want to double up then it will be 8, 4, 2...

    Please answer me..it make me confused.

  • #2
    Re: Logical Processor?

    You are correct that you are seeing 16 processors becuase VMWare counts Hyperthreading.

    Excellent reference: http://communities.vmware.com/docs/DOC-5101

    According to the article above it will treat the first 8 vCPUs as the actual CPUs, anything after will get a hyperthreaded CPU.

    ------------------

    In a simple view you are just giving Ghz speed to the VM.
    Lets assume you have a 2way quad 2.5Ghz (to make math easy)
    Total CPU speed (not counting Hyperthreading) is 20Ghz (or 8 x 2.5Ghz)
    VM 1 = 4 CPUs = 10Ghz
    VM 2 = 2 CPUs = 5Ghz
    VM 3 = 1 CPU = 2.5Ghz

    These are the MAX the system can use, not what they will use. It is probably not a best usage, but you could give each VM all of you processors and scale back if you really needed to.

    I run 6 VMs on each of my DL360s allowing for more than 150% CPU usage and my processors still only average 30% (Mostly Terminal Servers and SQL Server). My highest number was 60% as a spike.

    Hobie
    Last edited by Hobie; 21st August 2010, 03:13.

    Comment


    • #3
      Re: Logical Processor?

      If your VM will not be able to utilize more than one CPU - then allocating a second / fourth vCPU to the VM will not increase the performance - but there is a decent chance that it will degrade the performance of the VM.

      As a rule - most VM's will do fine with 1 vCPU - no need for the additional vCPU's
      Maish
      ----------------------------------------------------------
      Technodrone|@maishsk|Author of VMware vSphere Design
      VMware vExpert 2013-2010,VCAP5-DCA/DCD,VCP
      MSCA 2000/2003, MCSE 2000/2003
      A proud husband and father of 3 girls
      ----------------------------------------------------------
      If you find the information useful please don't forget to give reputation points sigpic.

      Have a good one!!

      Comment


      • #4
        Re: Logical Processor?

        Originally posted by Hobie View Post
        You are correct that you are seeing 16 processors becuase VMWare counts Hyperthreading.

        Excellent reference: http://communities.vmware.com/docs/DOC-5101

        According to the article above it will treat the first 8 vCPUs as the actual CPUs, anything after will get a hyperthreaded CPU.

        ------------------

        In a simple view you are just giving Ghz speed to the VM.
        Lets assume you have a 2way quad 2.5Ghz (to make math easy)
        Total CPU speed (not counting Hyperthreading) is 20Ghz (or 8 x 2.5Ghz)
        VM 1 = 4 CPUs = 10Ghz
        VM 2 = 2 CPUs = 5Ghz
        VM 3 = 1 CPU = 2.5Ghz

        These are the MAX the system can use, not what they will use. It is probably not a best usage, but you could give each VM all of you processors and scale back if you really needed to.

        I run 6 VMs on each of my DL360s allowing for more than 150% CPU usage and my processors still only average 30% (Mostly Terminal Servers and SQL Server). My highest number was 60% as a spike.

        Hobie
        Excellent explanation Thanks a lot..

        Comment


        • #5
          Re: Logical Processor?

          Originally posted by Maish View Post
          If your VM will not be able to utilize more than one CPU - then allocating a second / fourth vCPU to the VM will not increase the performance - but there is a decent chance that it will degrade the performance of the VM.

          As a rule - most VM's will do fine with 1 vCPU - no need for the additional vCPU's
          Excellent explanation Thanks a lot..

          Comment

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