Monday, June 6, 2011

Alternate Witness Server in Database Availability Groups

In this post we will look at the Alternate Witness Server - what is it?

The Alternate Witness Server provides a replacement witness server for a DAG to use after a datacenter switchover. When you are performing a datacenter switchover, you’re restoring service and data to an alternate or standby datacenter after you’ve deemed your primary datacenter un-usable from a messaging service perspective.

Although you can configure an Alternate Witness Server (and corresponding Alternate Witness Directory) for a DAG at any time, the Alternate Witness Server will not be used by the DAG until part-way through a datacenter switchover; specifically, when the Restore-DatabaseAvailabilityGroup cmdlet is used.

The Alternate Witness Server itself does not provide any redundancy for the Witness Server, and DAGs do not dynamically switch witness servers, nor do they automatically start using the Alternate Witness Server in the event of a problem with the Witness Server.

The reality is that the Witness Server does not need to be made redundant. In the event the server acting as the Witness Server is lost, it is a quick and easy operation to configure a replacement Witness Server from either the Exchange Management Console or the Exchange Management Shell.


  1. HI, i have following configuration for my exchange environment.
    Physical Servers-- mx-01 & mx-02
    mx-01 hosting mx-05 & mx-06, mx-02 hosting mx-03 & mx-04.
    mx-03 & mx-05 is cas/hub server while mx-04 & mx-06 is database server.
    For DAG mx-03\fsw is primary witness server & mx-05\fsw is alternate witness server.
    if mx-03 is switched off and that time if i switchover the database from one server to another server then it fails to mount. and database dismounts.

    while investigating i found that mx-03\fsw have some contents while mx-05\fsw don't have any content in fsw.

    Kindly let me know what is the and how to proceed further.

    Your help is much appreciated.

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  4. Check this out about Exchange data center HA Switch over and stretching DAG between sites.
    It is notes from engineers in the field doing data center switch overs for Exchange 2010 with tips and real word scenarios. It explains everything in step by step and examples.