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Interesting Exchange 2010 CAS question

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  • Interesting Exchange 2010 CAS question

    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.

    Simon Butler
    Exchange MVP

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