I am the Exchange Admin at a K-12 school district and plan on upgrading Exchange 2007 to 2013.  Currently I have 2 servers (CAS and Mailbox) running on a stand alone Hyper-V host (2008 R2).  There are 6 other servers running on the same host. We have about 900 users. Performance has been fine.  Last summer we set up a Windows Server 2012 R2 Hyper-V HA Cluster (boot to SAN).  We have 8 servers running on this cluster since then and the system has been stable. I plan on setting up 2 more servers on this HA cluster for the new Exchange 2013 upgrade.  I do not have any money in our budget for new hardware.  In fact, if I attempted to ask for any money, "they" will say we should drop Exchange and migrate to Google.  Any advice/recommendations on installing Exchange on a Hyper-V HA cluster?  Thanks.

You probably do not need to separate the CAS and Mailbox roles.  Consider installing a single server with both roles.

I agree with Ed.  You can probably get away with using multirole servers.  I would probably try and setup a node on each Hyper-V Host and configure a 2 node DAG to give me some kind of high availability (even though there are some inherited by the Hyper-V cluster itself) if I have the resources available.  

• Marked as answer by Mavis_HuangMicrosoft contingent staff, Moderator Friday, January 02, 2015 7:10 AM

Thanks.  I'm curious as to why not separate the roles.  Is it because it was not necessary back with Exchange 2007 or is it not necessary now with 2013?

Unless you're running a huge number of maximally loaded servers like Microsoft Online Services, the only reason I can think of to separate the roles is if you want to deploy a DAG and you need to use WNLB instead of a hardware load balancer.  In that case, you'll need to separate the roles since WNLB won't coexist with a Windows Failover Clustering, which is required for DAG members.

Microsoft is recommending that customers deploy servers with both roles.

Thanks.  Ok, I'll put both roles on the server.  So I can better understand...I remember when our consultant set up Exchange 2007, they told me they separate CAS from MB because it is more secure because only the CAS server gets NATed to an external IP, keeping the Mailbox server internal.   Do I need to setup an Edge Transport server? Or is only a single server all I need?

thanks again

Exchange 2013 CAS is stateless it wont be storing any user data as it used to in earlier version so CAS load is almost gone it just going to do a proxy and re-direction , hence it really a good idea to have a multirole on single box that i can help you to save $$ and if you any chance you plan to go with HA feature it would be good for DAG and 2 nodes in it (multirole) and probably you can do a DNS round robin for CAS.

In Exchange 2007 if you wanted to use mailbox database replication you had to separate the CAS role.  Maybe that's the reason.

Last question before I start a new thread with Edge Transport role questions...

Since I will be taking all your advice and will not separate the CAS and MB roles, should I consider setting up an Edge Transport server?

If you believe that the Edge Transport role offers you features you want or need, deploy it.  That's the sole consideration in my opinion.