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Advice needed for multi site CAS array

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  • Advice needed for multi site CAS array

    Hello,

    The title is probably a bit vague/inaccurate, so hopefully I can explain a bit better.

    Basically, I have a customer who has a lot of ADSL issues at one site (yes, they are going to move to a leased line at some point but not for a while and would like this functiionality anyway in case of other failures)

    They have 2 sites with 1 exch 2010 server with a database on each in a DAG. Their public facing CAS server is at the site that often goes down.

    The DAG works, but user's on the road who are using Outlook Anywhere, OWA or AS cannot then access their mailbox while the CAS server is unavailable.

    I'm thinking perhaps (budget permitting) putting TMG on a server up in the datacentre we use, but am not sure if the config would work. Firstly can you specify a primary public CAS server URL, and then configure a secondary in the event the first is unavailable?

    Do you need a CAS array to do this? As from what I understand WNLB and failover clustering will not work together.

    They've just invested in 2 x Exchange 2010 licenses + CALs and quite a lot on hardware with their previous IT company. Now their budget is almost depleted. I can't help thinking for the amount of users (less than 50) that Exchange Online could have been a better solution for them in this instance, unless they had a bit more to invest in their infrastructure...

    I would appreciate your thoughts

  • #2
    Re: Advice needed for multi site CAS array

    Let me first recap what I have understood. Your customer have 2 E2010 multi-role server spread about two different physical locations which are also 2 different AD sites. The mailbox role is configured as a DAG and for CAS/HT there is no high-availability option in place right now.
    There is no TMG configured for external access either.

    If the first site goes down which is Internet facing external users can't access their mailboxes.

    Until the configuration is a bit more clear I could only answer a few questions.

    Yes, WNLB and failover clustering will not work together on the same machines, you will need a hardware based NLB. If there are 2 AD sites configured a CAS array will not work at all.

    Some questions comes into mind as well.Why spread the E2010 server on 2 sites at first place?
    Which solution is used to publish Exchange to the internet?

    Comment


    • #3
      Re: Advice needed for multi site CAS array

      Hi FischFra

      Your first 2 paragraphs are correct.

      Yes, I would need a hardware NLB, if the 2 servers were in the same physical locations, but these guys want to still be able to work if a whole site is unavailable - which is often the case.

      The 2 Exch servers are in 2 physical locations for resiliency. Similar to having a failover datacentre, although the users in their 2nd office use the database on the server local to them.

      What solution is used to publish it? Exchange itself...? 443 points straight to it, if thats what you mean?

      They have Blackberry users as well, but I didn't want to confuse matters just yet...

      Comment


      • #4
        Re: Advice needed for multi site CAS array

        Personally what I would do is have all of the remote users on the Exchange server in the reliable connection site.
        Then have all external traffic go through that site.
        The unreliable site would not be exposed to the Internet.

        A CAS array isn't going to help here, although I would have one for each site anyway - your biggest problem is retro-fitting it.

        Simon.
        --
        Simon Butler
        Exchange MVP

        Blog: http://blog.sembee.co.uk/
        More Exchange Content: http://exchange.sembee.info/
        Exchange Resources List: http://exbpa.com/
        In the UK? Hire me: http://www.sembee.co.uk/

        Sembee is a registered trademark, used here with permission.

        Comment


        • #5
          Re: Advice needed for multi site CAS array

          Hi Sembee. I did see your blog article on CAS arrays - I will have to revisit.

          Is there no way to have a site resilient CAS array for mobile users? What about If money was no object?

          Another question too: Say for instance Bob works 3 days in the office at Site A (the unreliable connection site), but 2 days a week on the road. His mailbox would be stored in Site A's database, with a replica up to Site B.

          If external CAS was now pointing to Site B, would he get redirected to his replica mailbox, or does he still connect to Site A's primary copy? ie does a complete DAG failover have to occur before it uses the replica?

          If so, what then happens if the link is down to the primary site? (I'm sure the answer is for them to spend some money on a leased line...ha!)

          Thanks very much.

          Comment


          • #6
            Re: Advice needed for multi site CAS array

            A CAS array on its own has nothing to do with high availability. It is just a virtual name that can then be pointed to a different IP address, such as that which belongs to a network load balancing device.

            The only way to have something that works for mobile users to have their mailbox in a data centre, so that someone else is responsible for the Internet connections. In most locations connectivity redundancy is almost impossible, even if you have two ISPs the last mile is often the same. Although personally I live somewhere with both cable and xDSL, so I have more connectivity options than most of my clients!

            The replica of the mailbox is passive. Your data cannot be live in two locations. Therefore is a user goes to another site, they will just connect back to their own Exchange server (and thus the CAS array). The only time it would change is when you fail over and the virtual Exchange server name is pointing to another server.

            If the link is down to the primary site, then all users in the secondary site have no access to any mailboxes in that site.

            Simon.
            --
            Simon Butler
            Exchange MVP

            Blog: http://blog.sembee.co.uk/
            More Exchange Content: http://exchange.sembee.info/
            Exchange Resources List: http://exbpa.com/
            In the UK? Hire me: http://www.sembee.co.uk/

            Sembee is a registered trademark, used here with permission.

            Comment

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