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Explanation for Exchange 2010 Database Availability Groups

Exchange 2010 Database availability groups allow replication of mailbox databases for redundancy. It uses various Microsoft technologies to provide this service. DAGs take advantage of Windows server 2008 clustering, Log shipping technology, Shadow Redundancy and Incremental Reseeding. Exchange 2010 DAG uses Windows clustering that is different from Exchange 2003 and Exchange 2010. It uses Windows clustering to monitor heartbeat of each other; Exchange 2010 does not require the administrators to manage them at the cluster level.  Unlike Exchange 2007, in Exchange 2010, since a single mailbox database can be replicated across multiple servers, it is required that all mailbox database names are unique. Shadow Redundancy is similar to the Exchange 2007 transport dumpster function. Message that is sent to hub transport role was saved in the transport dumpster.
Requirements for Exchange 2010 Database Availability Groups:

  1. Two or more Windows Server 2008 Enterprise Servers
  2. Two or more NICs per server
  3. Exchange server 2010 Enterprise
  4. One File share witness per DAG

Exchange 2010 File Share Witness

Exchange 2010 DAGs are more of a replication technology than a traditional cluster but still uses some Server 2008 clustering functions to track each other heart beat. File Share Witness acts like a voting mechanism in a cluster. To create a File share Witness share, simply create a share on any server. DAG configuration will configure the permissions automatically.
How to create Exchange 2010 Database Availability Groups:

    • Open Exchange Management Console.
    • Organization Configuration > Mailbox.
    • Choose “Database Availability Group” tab.
    • Choose “New Database Availability Group.”
    • Follow on screen instructions.
    • DAG is created, but it has no member, follow below instructions to add member mailbox servers.
    • Organization Configuration > Mailbox.
    • Choose “Database Availability Group” tab.
    • Right click the properties of recently created DAG and choose manage database availability group membership.
    • Click Add and choose the mailbox server from the list. Then click manage.
    • Click finish.
    • Organization Configuration > Mailbox.
    • Right click on the database you want to replicate.
    • Choose “Add mailbox database copy.”
    • Follow on screen instructions, click finish.