Hi,
One of our client has Exchange server 2010 with Hyper-v and they are running two site DC and DR. Witness server are located in DC site with other physical server, this server is also running file server service. When they down DC's Exchange server then Exchange server are running fine from DR site. But when they down witness server after 1 to 2 hour's later then DR Exchange Database is dismounted state and Exchange server is not working. Their High availability of exchange server with DAG for mailbox. Why this problem occur.