Primary Site Failure and Backup Site Activation

Activation of the Disaster Recovery site begins with
verification of directory services and DNS resolution. Because the DR site
should already contain a directory server that is also hosting Active Directory-integrated
DNS, these services should be healthy, current, and largely unaffected by the
outage of the production site.

There are three basic steps that you complete to
perform a data centre switchover, after making the initial decision to activate
the second data centre:

1. Terminate a
   partially running data centre:   This
   step involves terminating Mailbox Service in the primary data centre, if any
   services are still running. This is particularly important for the Mailbox
   server role because it uses an active/passive high availability model. If
   services in a partially failed data centre aren't stopped, it's possible for
   problems from the partially failed data centre to negatively affect the
   services during a switchover back to the primary data centre.
2. Activate the
   Mailbox servers:   This step
   begins the process of activating the second data centre. This step can be
   performed in parallel with step 4 because the Microsoft Exchange services can
   handle database outages and recover. Activating the Mailbox servers involves a
   process of marking the failed servers from the primary data centre as
   unavailable followed by activation of the servers in the second data centre.
   The activation process for Mailbox servers depends on whether the DAG is in
   database activation coordination (DAC) mode. For more information about
   database activation coordination mode, see Understanding Datacenter Activation
   Coordination Mode
3. Activate the other
   server roles   This involves
   using the URL mapping information and the Domain Name System (DNS) change
   methodology to perform all required DNS updates. The mapping information
   describes what DNS changes to perform. The amount of time required to complete
   the update depends on the methodology used and the Time to Live settings on the
   DNS record (and whether the deployment’s infrastructure honours the TTL)

These steps are described in more detail in the following
        
Terminate a partially running datacenter

If any DAG members in the failed datacenter are still
running, they should be terminated. When the DAG is in DAC mode, the specific
actions to terminate any surviving DAG members in the primary datacenter are as
follows:

1. If the production mailbox servers are online and accessible, run the
   following commands in the production datacentre:

1. If the production mailbox servers are offline, run the following
   commands in the production datacentre:

1. In the DR site run the following command:

1.1.2         
Activating Mailbox Servers

When the DAG is in DAC mode, the steps to complete
activation of the mailbox servers in the second datacenter are as follows:

1. Stop the Cluster Service on the DAG member in the DR Site (MBX SERVER
   NAME).
   1. a.      
      Net stop Clussvc or use
      the Services snap-in
   2. Restore the DAG in the DR site as follows:

Bring databases

online:

Verify that all databases are mounted.