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.