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:

Stop-DatabaseAvailabilityGroup
–Identity DAG –MailboxServer MBX SERVER NAME 1

Stop-DatabaseAvailabilityGroup
–Identity DAG –MailboxServer MBX SERVER NAME 2

 

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

Stop-DatabaseAvailabilityGroup
–Identity DAG –MailboxServer MBX SERVER NAME 1 -ConfigurationOnly

Stop-DatabaseAvailabilityGroup
–Identity DAG –MailboxServer MBX SERVER NAME 2 -ConfigurationOnly

 

  1. In the DR site run the following command:

Stop-DatabaseAvailabilityGroup
–Identity DAG – ActiveDirectorySite SITE-A -ConfigurationOnly

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:

Restore-DatabaseAvailabilityGroup
–Identity DAG –ActiveDirectorySite EXCH-DR

Set-MailboxServer
–Identity MBX SERVER NAME –DatabaseCopyAutoActivationPolicy Unrestricted

      Bring databases

    online:

Get-MailboxDatabase
| Move-ActiveMailboxDatabase -ActivateOnServer MBX SERVER NAME

Verify that all databases are mounted.