No announcement yet.

Virtualised Exchange within a DAG

  • Filter
  • Time
  • Show
Clear All
new posts

  • Virtualised Exchange within a DAG

    Hi everyone,

    We are currently in the process of setting up a new system:

    2 x ML370 G6 - Server 2008 R2 Datacentre, running Hyper V
    1 x HP P2000 G3 SAN (Fibre Channel)

    The physicals are acting as a HV host, and a number of VMs will be set up in a failover cluster. There will be an Exchange Server on each physical - not setup in the live migration cluster and on different volumes on the SAN.

    My question is, how does the DAG bit work, as I've seen that it uses Failover Clustering (or maybe just 'elements' of failover clustering)

    - If that's so, and the Exchange servers are virtualised, do they need a quorum?
    - How can this be achieved using a FC SAN?
    - Or will it have to use iSCSI?
    - Can it not use a file share witness?

    It's the next part of our testing phase and it would be nice to get other people's input beforehand

    Thanks in advance.

  • #2
    Re: Virtualised Exchange within a DAG

    DAG is based on failover cluster techniques from Windows - virtualized or not, every cluster needs a quorum in one form or another. Assuming you set up a majority node set you can or better you have to use file share witeness as well.

    Even if the DAG setup is done in Exchange it's still the Windows cluster service behind so the basics are still the same.

    Regarding which disks to use you might want to read about Exchange 2010 and virtualization, I think it make it clear what you are able to use and what not.

    Since I'm not an fan of virtualizing mailbox servers I can't speak about practical implementations though.

    Btw. while you are thinking about the DAG you might also think about high availability for the CAS role.


    • #3
      Re: Virtualised Exchange within a DAG

      Hi FischFra, thanks for your reply.

      I think the main confusion really for me is on our 2 physical hosts, we have a failover cluster, which has a quorum on one of the volumes on the SAN - published to it via Fibre Channel.

      As Exchange will be virtualised, we can't publish FC disks to it for a Quorum. iSCSI is probably out of the equation too, as it will require purchasing more equipment. Could we just use a file share witness on another server as the Quorum?

      Also just out of interest, why are you not so keen on virtualising mailbox servers?

      Would the HA element for CAS be done through Failover clustering or would we need a hardware load balancer?


      • #4
        Re: Virtualised Exchange within a DAG

        Majority node set clusters don't need a dedicated quorum device if this is your question. In order to run, a majority of the nodes have to be up and running this is where the file share witeness comes into play.

        Depending on the number of mailboxes which should be supported by a mailbox server you need the appropriate ressources which makes virtualization sometimes or most of the times pointless.
        Virtualization adds another layer of complexity to the installation which makes troubleshooting a lot more difficult.

        Regarding HA for CAS, it's called CAS array for the AD site and it's done with a hardware loadbalancer or NLB.


        • #5
          Re: Virtualised Exchange within a DAG

          The biggest problem we have had in the Exchange community is people trying to use DAG and whatever fail over technologies are used by the virtual technology. The simple rule is use either DAG, or the VM based technology, but not both.

          Personally I see no problems in virtualising mailbox servers and every Exchange 2010 deployment I have done has been in to a VM. Once the VM is built, from a troubleshooting point of view it becomes practically a null issue. Although I use VMWARE Exclusively, I have no HyperV deployments at all.

          For an overview of the DAG setup, I like this blog posting by another Exchange MVP.

          It goes over the setup process quite nicely, and explains a lot of the concepts behind it.
          If you haven't already, do a setup in a lab - you can do it with three virtual machines, four if you want simulate a site replication scenario. Its one of those things that once you have done it, and can get your head away from the clustering part, it becomes easier.

          Simon Butler
          Exchange MVP

          More Exchange Content:
          Exchange Resources List:
          In the UK? Hire me:

          Sembee is a registered trademark, used here with permission.


          • #6
            Re: Virtualised Exchange within a DAG

            FischFra/Sembee - Thank you guys very much.

            Test lab is up and DAGs seem to be doing what I need them to do.