Merge Active Directory Sites to facillitate Automatic Failover of Exchange

We have 2 locations connected via site-to-site VPN. Internet speed is about 3MB, ping times between locations is about 70ms. They are currently in separate Active Directory sites, separate subnets, but one domain. We want to have Exchange in failover mode and would prefer not to have to go through the manual failover process if we don't have to. What would be the pros and cons, and the process to merge the sites if the pros outweigh?

The forest is native mode, 2003 R2 DC in 1 location and 2008 R2 DC in the other. We are adding a 2012 server to the first location and Exchange 2013. I understand with 1 site we need a member server to act as a DAG witness.

Thank you.
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jconklin-ansinc-netAuthor Commented:
suriyaehnop- thanks I was hoping for something a little more specific to my situation as described. my main question is whether it makes sense to merge the 2 AD sites and if so how?
Simon Butler (Sembee)ConsultantCommented:
I wouldn't merge the two sites.
Leave both sites as they are.
However I would also discourage you from using automatic failover. The most common cause of inter-site problems is the link dropping. If you have automatic failover you will find that things don't work exactly as you planned.

Furthermore, a DAG in Exchange 2010 only protects the databases. It does nothing for the clients. Therefore you will need a CAS array and if you want autoamtic failover you will also need a hardware load balancer.

When planning this though, it helps if you start with the scenarios that you want to cover, then adjust from there. The scenario planning I do for a company in central London is very different to rural Scotland!

jconklin-ansinc-netAuthor Commented:
I'm going to move forward without merging the sites. It doesn't seem that the question was answered.

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jconklin-ansinc-netAuthor Commented:
the answers didn't really address anything concrete. i've decided to just go ahead without merging the sites.
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