1 Reply Latest reply on Aug 2, 2016 2:21 AM by Alim786

    Reservation vs dedicated resources

    mfx201110141 Novice

      In regards to using reservations, I have a question that I'm hoping to get your input to.

      Some quick background information:

      Scenario 1:

      Standalone host, without overcommitment on CPU, manually keeping the pCPU:vCPU ratio below or on 1:1

       

      Scenario 2:

      A overcommitted DRS cluster (CPUwise), and some VMs with reservations.

       

      As I understand from https://www.vmware.com/support/developer/converter-sdk/conv55_apireference/vim.ResourceAllocationInfo.html,

      then in Scenario 2, if I reserve CPU to a given VM, then if the VM does not actively use the entire reservation, then other VMs can make use of the resources.

       

      And now to my question: if the VM with the reservation increases its demand, will the resources be "given back" to the VM instant, or will there be a tiny delay in access to the resources?

      The reason for my question is that when running VOIP applications (such as Microsoft Skype For Business) they tend to be very sensitive  to CPU contention and the vendor recommends not overcommiting CPU in clusters containing these VMs.

      If I compare the 2 scenarios, will the response time for access to CPU resources be the same, or will Scenario 1 perform better?

        • 1. Re: Reservation vs dedicated resources
          Alim786 Hot Shot

          Your question - "if the VM with the reservation increases its demand, will the resources be "given back" to the VM instant, or will there be a tiny delay in access to the resources?"

          Answer - "As long as the VM is "right-sized", it will get all the resources it demands."

           

          Your question - "If I compare the 2 scenarios, will the response time for access to CPU resources be the same, or will Scenario 1 perform better?"

          Answer - "It depends. If you are happy to manage the resources of the Stand-Alone Host yourself, then that is the safest option. The whole point of DRS is to make use of all the resources of the Hosts so that there is no wastage and reduces the TCO and increases ROI. At the end of the day, capacity management procedures must be in place to make sure you are not reaching saturation and resource contention.

          VCP6-DCV, VCP5, CCNA, MCTS 2008R2, MCSA 2008R2, CCA, ITIL.
          Please mark answer helpful or correct as appropriate.