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Ok I've got 2 exchange 2010 servers that run client access/hub transport/mailbox roles and one exchange 2010 server running just client access/hub transport roles and acts as my bridgehead. The two mailbox servers are running one database setup in a DAG. Server A shows the DB Mounted and Server B shows Healthy. If I reboot Server A via windows GUI Server B switches from healthy to mounted and I see hardly any interruption in service using Outlook 2007. Server A shows "Service down", then "Failed" then "Healthy" and leaves the DB mounted on Server B. This is how it should work, so far so good.

Now if I test Server A being shut down cold, or unplugging both nics from network to simulate failure, Server B switches from Healthy to Mounted and server A switches to "Service Down" but my outlook client never connects to the DB mounted on server B! I can connect to server C (client access/hub transport) and get to my email and even send new email out, but incoming email doesn't deliver until Server A is brought back online and it's DB goes back to Healthy status.

So I don't understand why it auto fail-overs when I reboot the server with the mounted DB copy, causing very little outlook 2007 hiccup if any. But when I shutdown or DC the mounted DB server it DOES mount the healthy copy but outlook 2007 clients can't connect..

I hope the picture I'm trying to paint makes some sense, it's driving me a little batty. Any help would be appreciated!

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Oh and oddly enough if Server B has the mounted copy and server A has the healthy copy, I CAN turn off server B and it fails over to A without issues with outlook 2007 clients connecting... – Richard Mar 10 '10 at 21:48
Is it possible the problem is all three servers are running hub transport/client access roles? The one I'm calling a bridgehead server should be the only one with these roles and just keep server A and B as mailbox servers? – Richard Mar 11 '10 at 13:08

I think you need to setup a cas array. Then set the database to use this array. Then do load balancing with a hardware load balancer or 2 dedicated cas servers with nlb. I'll edit this later when at a computer to give more details. This should give you enough to google though.

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I think the issue is related to the Client Access Server role, specifically the RPC Client Access Server.

I'm currently seeing the same thing as your original post in my environment. IF I stop the Microsoft Exchange RPC client Access Service one server B then I can't access the mailbox no matter which DAG member is mounted.

Unfortunately I don't have a clear solution yet. I think the trick involves load balancing the Client Access Server roles however you're not supposed to have NLB and DAG on the same server. So you'd either need to move the CAS roles to two other servers or use a hardware device to load balance.

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Hey thanks for the response! I sort of found out why it was broken and you're pretty much right on the money. I installed my exchange servers in a reverse order, first installing my mailbox servers with CAS/HT roles included before installing the 3rd HT/CAS server. I thought I could just uninstall the HT/CAS roles from the first two mailbox servers and the exchange environment would be smart enough to configure the organization to use the new and last remaining CS/HT server, but turns out you have to move the responsibility with the management tool before anything works. – Richard Mar 29 '10 at 16:46

For Exchange 2010 you need to create a CAS array, that will handle incoming user traffic, there are some additional settings required. Detailed explanation here.

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