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3 Servers, Trying to figure out best layout

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  • 3 Servers, Trying to figure out best layout

    I have a client that has exploded in size over the past year. They currently have a single Exchange 2010 server with all roles. Currently about 400 mailboxes and 900gb of mail. Growing approx 300GB/4 months. The server has 4 virtual cores, 12gb ram. They are in our hosted environmental and all users connect via RPC/HTTPs or OWA.

    They have ok'd 2 more servers and rebuilding the current one to remove some latent issues. I am trying to figure out the best layout of the servers and have come up with 2 options:

    1. 1 CAS server with 2 Database server. Servers would have DAGs between them and the primary/secondary split based on size for each DB

    2. 2 CAS servers with 1 DB server. Create DAGs between the DB and CAS servers and have the CAS have half of the databases in secondary mode.

    Any help I can get would be greatly appreciated.

  • #2
    Re: 3 Servers, Trying to figure out best layout

    someone else will come along with something better than what i say

    but i'd go one CAS, two MBX.

    the mailbox role is more disk intensive than cas. that's my reasoning
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    • #3
      Re: 3 Servers, Trying to figure out best layout

      If its hosted, do you have any concerns that will require you to have two CAS servers -- you will need some load balancing for them anyway.

      However I like your idea of sharing roles to make them all redundent -- IMHO maybe
      1 x CAS / HT
      1 x MB / Backup CAS
      1 x MB / Backup HT

      You could split the active databases between the two MBX servers (passive on the other) so all components are redundant. You would also need to consider DC/GC placement to ensure they are highly available.
      However, this may be an area where some proper consultancy is required
      Tom Jones
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      Ossian Ltd

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      • #4
        Re: 3 Servers, Trying to figure out best layout

        If you want redundancy you will need another server.
        This would allow you to have two Mailbox servers and two CAS/Hub. There isn't really the concept of "backup" CAS or Hub transport roles. All hub transport servers will be used, and the CAS servers will take a pounding due to the new configuration layout. You might get away with a single CAS/Hub transport server if it is well specified, but unless you are going to use a third party load balancer, you can't put CAS on to one of the mailbox servers as well and have both being used, because WNLB is not supported on the mailbox role.

        If they are in the same data centre then I would have mailboxes on both servers, in Active/Active. Ensure that the servers have enough space to be able to cope with all mailboxes on the same server.

        The biggest problem you are going to have is the clients. Unless you had the foresight to configure a CAS array to begin with, you will probably need to keep the existing server, or the client is going to have to find a way to touch every Outlook installation. Even if you move mailbox, the Outlook client will not update, because the CAS server hasn't changed. Outlook now connects to the CAS server, not the mailbox server directly.

        I would suggest that you immediately configure a CAS array so that new Outlook installations are starting to use that, and ask the client to touch every Outlook installation they go near (repair profile) to reduce the numbers that will need doing when the servers are changed round. A CAS array is just a DNS entry at its core, so you can point it at the existing server.

        Simon Butler
        Exchange MVP

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