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  • vSphere 5 Datastore Planning

    We are implementing a 2 host vSphere 5 installation using a P2000 FC MSA. This will virtualize about 8 servers, including Exchange. On*the MSA the RAID array is set at the higest level (vDisk). Volumes (LUNs) are partitioned out of the vDisk. *We are planning on implementing this by just splitting the vDisks across the controllers making two 1.2tb RAID5 arrays. From there create a 500gb volume(LUN) from each vDisk to use as VMFS datastores for the VMs leaving room for additional storage when needed. A few questions:
    *
    If the physical server would normally have 2 partitions(OS c: and DataVolume d would we create two VMDK virtual disks in vmware for the VM vs one and partitioning within the VM?
    *
    Can the OS c: be on a different datastore than the data volume d: ?
    *
    For exchange, considering the amount of users is < 50 and our current DB size is small, is it acceptable to create three VMDK virtual disks vs 3 additional LUNs?
    *
    Many thanks in advance for any assistance.

  • #2
    Re: vSphere 5 Datastore Planning

    Your logic is good.

    But useless until your assess the IO's your storage can deliver and the IO's your VMs require.

    Also don't forget to factor in the RAID 5 write penalty, that is for every single write IO, the storage back end does 4 IOs. The formula is: (TOTAL IOps % READ) + ((TOTAL IOps % WRITE) 4)

    x4 for RAID5
    x2 for RAID1


    Microsoft has a tool to assess servers called Microsoft Assessment and Planning Toolkit.
    VMware has a tool to benchmark the storage called VMware I/O Analyzer.

    Freelance, Business Owner, Virtualisation & Cloud Computing Fan Boy, VCP4/5/Cloud, VCAP4/5-DCA/DCD, vEXPERT '10-'14, EMCCA-Specialist, VMware Alumni.

    Comment


    • #3
      Re: vSphere 5 Datastore Planning

      Thank you for your reply. The p2000 has 12 15k SAS drives and two controllers. The drives should be split between the controllers, which was the reasoning for RAID5 (more spindles). The understanding was that the penality would be negligable for these drives. Currently, the physical servers are all RAID5 and the performance is good.

      What are your thoughts on the VMDKs? Should we have two (one for c: and one for the data volume d or one large VMDK and partition in the os?

      Can they be on different datastores?

      Again, many thanks in advance for any insight.

      Comment


      • #4
        Re: vSphere 5 Datastore Planning

        As PiroNet writes it would be good to figure out your I/O requirements first; then incorporate capacity and availability requirements. We don't use Exchange in our particular environment, however we have generally benefited from multiple VMDK files per virtual machine. The way we add virtual disks to our Windows VMs is via additional VMDK files.

        The reason a unique VMDK file per disk has been beneficial in our case is because if we want to move, as you mention, one of the VM's disks from array #1 to array #2 without moving all of the VM's disks then we are now able to do so. They can exist on different datastores and in some instances you may want them on different datastores. Keep in mind that using multiple datastores per VM adds complexity to any disaster recovery plan you might have designed in the early stages of virtualization. This is especially true when those datastores reside in separate physical arrays and storage chassis.

        There are some DR considerations that are not broached in your original question. Keep in mind what you are licensed to do; storage vMotion and vSphere Data Protection can offer you some flexibility that may come in handly, however they may or may not agree with existing policy and infrastructure parameters.

        Hope that helps,
        Justin

        Originally posted by windows_help View Post
        Thank you for your reply. The p2000 has 12 15k SAS drives and two controllers. The drives should be split between the controllers, which was the reasoning for RAID5 (more spindles). The understanding was that the penality would be negligable for these drives. Currently, the physical servers are all RAID5 and the performance is good.

        What are your thoughts on the VMDKs? Should we have two (one for c: and one for the data volume d or one large VMDK and partition in the os?

        Can they be on different datastores?

        Again, many thanks in advance for any insight.

        Comment


        • #5
          Re: vSphere 5 Datastore Planning

          Originally posted by windows_help View Post
          Thank you for your reply. The p2000 has 12 15k SAS drives and two controllers. The drives should be split between the controllers, which was the reasoning for RAID5 (more spindles). The understanding was that the penality would be negligable for these drives. Currently, the physical servers are all RAID5 and the performance is good.

          What are your thoughts on the VMDKs? Should we have two (one for c: and one for the data volume d or one large VMDK and partition in the os?

          Can they be on different datastores?

          Again, many thanks in advance for any insight.
          With RAID5 you would indeed benefit from more spindles which improves reads actually. So if the I/O profile of your workloads is 75% Reads, you're good I would say.
          On the opposite, if you have a 75% Writes I/O profile, well this is not optimal.

          RAID5 is fine with the actual setup as you mentioned but it is a 1:1 ratio, one OS accessing its own dedicated spindles. Going for a shared storage, you share the spindles with many VMs and most probably the I/O pattern is highly random. Most probably you'll amplify RAID5 write penalty actually... And suddenly what seemed OK on a physical server is a nightmare on a shared environment.

          Splitting the VMDK's is fine if you also have datastores with different IO characteristics. A RAID5 datastore for C: and a RAID10 for D: for example
          Otherwise, to avoid the management overhead, just keep VMDKs together.

          Also, I often privilege multiple 'small' datastore than few large ones.
          Having multiple datastores increases parallelism and number of queues.

          So again, my advice is you first profile your I/O requirements, then benchmark your storage with different RAID configurations.

          Freelance, Business Owner, Virtualisation & Cloud Computing Fan Boy, VCP4/5/Cloud, VCAP4/5-DCA/DCD, vEXPERT '10-'14, EMCCA-Specialist, VMware Alumni.

          Comment


          • #6
            Re: vSphere 5 Datastore Planning

            Thanks again for your input, it is very helpful. The P2000 has two controlIers and should have at least two arrays to utilize both, otherwise one is always in standby. Which is why we were trying to make the most out of the available disks. I understand the IOPS requirement is very important, thank you. We are now beginning to re-think the deployment. Looking at possibly using a 6 drive RAID10 and a 4 drive RAID5, 900gb each and monitor the VMs for preformance issues. We have enterprise plus for VMWare, I suppose we could always use Storage DRS to handle the VM placement. Would that help?

            Thanks again for your help.

            Comment


            • #7
              Re: vSphere 5 Datastore Planning

              Originally posted by windows_help View Post
              Thanks again for your input, it is very helpful. The P2000 has two controlIers and should have at least two arrays to utilize both, otherwise one is always in standby. Which is why we were trying to make the most out of the available disks. I understand the IOPS requirement is very important, thank you. We are now beginning to re-think the deployment. Looking at possibly using a 6 drive RAID10 and a 4 drive RAID5, 900gb each and monitor the VMs for preformance issues. We have enterprise plus for VMWare, I suppose we could always use Storage DRS to handle the VM placement. Would that help?

              Thanks again for your help.
              Storage DRS for initial placement and SIOC would be both of a great help here.

              If you deploy Windows VMs prior Windows 2008, pay attention to disk misalignment as well.

              Freelance, Business Owner, Virtualisation & Cloud Computing Fan Boy, VCP4/5/Cloud, VCAP4/5-DCA/DCD, vEXPERT '10-'14, EMCCA-Specialist, VMware Alumni.

              Comment

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