I currently have two sites where one is just a spoke that talks back the exchange server at the main site. Luckily I'm finally getting some bandwidth between the two and I'm trying to figure out a good way to have HA over the link.

We currently use Exchange 2007 and are looking at moving to exchange 2010 so I thought this was a perfect time to think about this. I've been doing some reading on DAG and I find it very interesting.

My issue comes down to that each site has its own active directory site but currently the spoke site uses outlook anywhere and doesn't really use their domain for anything except login.

My main qusetions is if I manage to have two servers, one sitting at site 1 and one at site 2, one is going to be a passive server and the other is going to be an active? So if site one goes down, do I just have another mx record with a different priority? So that when DAG notices it will kick on the server and start to respond?

We already have a secondary mailserver holding our mail but I'd like for a quick response as email is our current lifeblood for many of our products.


Your question is really two, and is easier to digest if you think about it in terms of each Exchange role.

You have a mailbox role, which supports DAG's, where you can have each site with it's own mailbox DB copy. Users using Outlook Anywhere will connect through CAS role so you have to think about how that is affected by server outage.

Then you have the hub role, which is what uses DNS MX records for controlling incoming SMTP mail. If you placed the hub rule on each server then you would want two MX records for incoming mail so if one went down the other would capture it.

The most redundant yet complex scenario is where both sites have Internet connections for incoming mail and remote access so if either site went down people could still use email over the Internet.

Don't assume putting a server on a 2nd site is automatically better. I much prefer central consolidation of servers (two redundant exchange servers side by side) if my requirements allow it. Sometimes admins put a 2nd box off site just because they can, when they realize the complexity and bandwidth issues they wish they hadn't after the fact. I also wouldn't put Exchange anywhere I couldn't be sure of physical security. Good luck!

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