Question : Exchange 2010 DAG becomes unavailable on second site

Hi, I’m having problems setting up an exchange 2010 DAG over two sites using just two exchange servers. If I shutdown one of the exchange servers. The DAG works as expected; I can access the database on the server which is still up, and I can activate the database which has been replicated (passive copy). I have autofailover turned off.

My problem comes if the internet between the sites fails

The site which has the witness server still works and i can access the database which is mounted, and the passive copy can be activated if needed. But on the second site, the DAG becomes unavailable and its mounted database reports it’s failed, and no clients can connect. When the internet comes back up, the failed database is remounted and outlook clients can connect again

I think the reason for the mounted database to fail, is the cluster manager can’t connect to the DAG, the DAG becomes unavailable on the site which doesn’t have the witness server.

Current setup
2 sites, siteA: 10.0.0.0/24 siteB: 10.0.5.0/24
both servers are running all roles. One on each site
One DAG which has two mailbox servers, each has one mailbox database
The DAG has two IP addresses 10.0.0.136 and 10.0.5.136
It has the witness server set to witnesssiteA  and a alternative witness server set to witnesssiteB

Answer : Exchange 2010 DAG becomes unavailable on second site

This behavior is as it should be.

If you use 2 Exchange-Servers and 1 File Share Witness only the site that has the majority can run the DAG.

By design you're not able to run the 2nd Database in the 2nd Site while the 1st Site is running.
DAG is Windows Cluster and if you have both sites up and running the same time and the internet connection everything would break.

There is one feature to run both mailboxes in one site without majority. It's called Datacenter Activation Mode.
As today this only works with 3 DAG-Servers. Starting with Exchange 2010 SP1 Microsoft said that this will be supported with two Exchange Server within a DAG. Never the less it is not supported to run one Database in one site while you're internet connection is failed.
http://technet.microsoft.com/en-us/library/dd979790.aspx