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Exchange DAG Means Disable VMotion For Mailbox Server

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  • Exchange DAG Means Disable VMotion For Mailbox Server

    I read that if you have Exchange setup with a Database Availability Group, then VMotioning one of those servers breaks DAG.

    The solution is to disable VMotion for those VM's and fix a particular mailbox server to a particular ESX host.

    When I thought about this, it occured to me that if a VM is not using VMotion (or any of the features that rely on it like HA and DRS), then there is no reason to store the VMDK on the shared storage.

    In fact, the VM files could be stored locally to the host. The reason being is that you would be running 2 separate mailbox servers that would fail over as per the Exchange mechanisms.

    I think this would also apply if I wanted, for example, to setup a MSCS cluster where each VM node is on a different ESX host.

    My question is, what is the best local storage configuration for an ESX host if you intend to store VMDK's and snapshots locally, while still having that host participate in a VMotion cluster?

    I'm assuming a small RAID-1 LUN0 for the hypervisor, and a whatever-size RAID-5 LUN1 for the VMDK's/Snapshot's.

  • #2
    Re: Exchange DAG Means Disable VMotion For Mailbox Server

    Personally I would keep it on shared storage.
    If the server fails for whatever reason, you might loose the data. With shared storage you always might have the option to manually power it up again on a different server. Also I noticed that shared storage might be actually faster, but that might rely on your local storage.
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    • #3
      Re: Exchange DAG Means Disable VMotion For Mailbox Server

      If you want that Host to participate in a DRS/HA cluster then the VM's that you want to portect will have to be on shared storage.

      Regarding what is the best layout for Local ESX host storage if you want to host the VM's locally - then you will have to balance between performance and redundancy needed.

      Raid 5 is most probably your best bet, but I would not go for SATA disks though
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      • #4
        Re: Exchange DAG Means Disable VMotion For Mailbox Server

        Thanks for the comments. Further reading supports your suggestions of keeping VMDK's on shared storage, even for VM's not participating in VMotion, et. al.

        But for the Exchange servers in particular though, the case could be considered different as there would already be a failover VM on the other ESX host.

        That is, DAG requires 2 servers so that if the primary fails, the database will remain accessible. So if the primary ESX host fails, Exchange will switch to using the secondary VM on the secondary ESX host to continue operations, without anything being done by vCenter.

        Essentially, losing the primary ESX is akin to losing the primary physical Exchange DB server.

        Saying that, it just makes it easier to maintain snapshots and perform updates if the Exchange DB VM's involved in DAG are on shared storage.