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Interesting Exchange 2010 CAS question

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  • Interesting Exchange 2010 CAS question

    Environment:
    SiteA contains CAS1, HT1 and DAG1
    SiteB contains CAS2,HT2 and DAG2.

    Lets says primary site is siteA and SiteB is for DR. All users are on DB1 which has a copy on DAG1 and DAG2? What if CAS1 fails?

    - Will users in SiteA get automatically redirected to CAS2 automatically?

    My understanding is that you need have a CAS server in every site ? How does the client (outlook 2007) know to connect to CAS2 ?

  • #2
    Re: Interesting Exchange 2010 CAS question

    Without additional hardware, automatic failover of the clients will not happen. DAG protects just the data, nothing else.

    I have compared it to an non-driving millionaire having a chauffeur driven car, owning a second car as a backup, but having no plan if the driver was to be unwell.

    You have two choices.
    Both of which require you to setup a Client Access Array, along with the additional headache of getting the clients to use the CAS array instead of the real CAS server address.

    1. A DNS entry, which you have to update manually in the event of a failure. This is the cheapest option. With a short TTL time on the DNS entry, clients will pick it up very quickly.
    2. A third party external load balancer.

    You can't use Windows NLB as that is not supported on the same system as a DAG. If you wanted to use NLB you would have to split the CAS role on to separate servers.

    http://blog.sembee.co.uk/post/RPC-Cl...ess-Array.aspx

    Simon.
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    Simon Butler
    Exchange MVP

    Blog: http://blog.sembee.co.uk/
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