ESXi

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  • 1.  mapping ration from pCPU to vCPU

    Posted Nov 22, 2017 10:23 AM

    In my ESXi 6 .0 cluster, the number (100) of physical CPU is bigger then vCPU number (300) so I ask myself if this this configuration is right or it's necessary to have mapping one to one (pCPU to vCPU) Is there specific ratio for this mapping in Vmware doc?!

    I thought to monitor CPU resources on each hosts in performance tab where every host is using about 25% of cpu. Suggestions ?!



  • 2.  RE: mapping ration from pCPU to vCPU

    Posted Nov 22, 2017 10:33 AM

    There are no recommendation from VMware based on what the vCPU to pCPU ratio should be .

    However the metric with this this ratio is closely monitored is the CPU Ready value.

    lot of factors are involved.

    1) nature of Machines

    2) PCPU speed

    3) Applications etc

    read the below KB and focus on CPU stats.

    VMware Knowledge Base

    VMware Knowledge Base



  • 3.  RE: mapping ration from pCPU to vCPU

    Posted Nov 22, 2017 12:10 PM

    For specific vm, which has n.4 vCpu, "%USED" value reached about 200% and it's lower then %RUN value, it means vm is using 2 cores of 4?



  • 4.  RE: mapping ration from pCPU to vCPU

    Posted Nov 22, 2017 12:54 PM

    It doesn't mean that the vm is using 2 cores of 4.  its means that there is enough CPU time available for all 4 threads coming from the VM to get executed.

    if the %ready value is high that means the vCPU threads are ready to run and waiting for CPU time on the actual physical core.

    as long as these values are healthy there there is no issues with your vCPU allocation..

    having said that over allocating vCPUs to VMs is also not good as there is additional scheduling overhead for every vCPU you add.

    VMware recommends starting with 1 vCPU and increasing the value as per the needs. If you have concrete sizing done and believe that you will need 4 vCPU than its a design requirement



  • 5.  RE: mapping ration from pCPU to vCPU

    Posted Nov 22, 2017 01:10 PM
    having said that over allocating vCPUs to VMs is also not good as there is additional scheduling overhead for every vCPU you add.

    VMware recommends starting with 1 vCPU and increasing the value as per the needs. If you have concrete sizing done and believe that you will need 4 vCPU than its a design requirement

    infact I suspect number of vCPU was overrated and and I'd like understand if this VM is using all vCPU and how it's using them (percentage).