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vmichFlag for United States of America

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exchnage 2010 DAG and CAS array

Do I need to have a CAS array with a DAG setup in exchange 2010 or the question should be, is it neccessary?
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Suliman Abu Kharroub
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For full high available, you need at least  4 servers: 2 CAR array and 2 DAG members.
it all depends on what you are trying to achieve what is necessary is to have a CAS and  HUB in each site where you have a Mailbox.

the correct answer to your question is NO, a CAS array is not necessary but of course it will provide redundancy.

What Sulimanw said is not perfectly true, you could have only 2 servers running cas/hub and mailboxes assuming you have an external load balancer
For clarity, if you have one AD site, with one Physical site, you can have a DAG cluster with just one CAS server. However, this presents a single point of failure. The CAS array with a DAG cluster solution allows you to have a solution that allows up to half the servers in your environment to fail without impacting service. With a Single CAS server and a DAG cluster, if you lost the CAS server, you're down, but you can lose one of your Mailbox servers without impacting users.
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Simon Butler (Sembee)
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