File Share Witness in Exchange Server 2010

As we know, Exchange Server 2007 supported three different kind of high availability methods which varied from the single server to across multiple Exchange servers. And then, Exchange Server 20010 introduced Database Availability Group (DAG) which is essentially a collection of at least two and maximum 16 mailbox servers to achieve the high availability.

You should be familiar with the term, File Share Witness (FSW) if you have already implemented the CCR in the Exchange 2007 environment. As the name suggest, file share witness is a file share residing on the third server outside of the DAG for ensuring quorum availability in the cluster. We can provide the file share witness directory and share name while creating the DAG.  Unlike Exchange 2007, where Microsoft recommended hosting file share witness on the Hut Transport server, Exchange 2010 provides you full control to host file share witness on non-Exchange Server as well, but you have to add the Exchange Trusted Subsystem Universal Security Group to the local Administrator Group on the FSW Server.

You can configure the FSW and FSW directory during DAG creation as shown below:-

New-DatabaseAvailabilityGroup -Name DAG01 -WitnessServer ACENT001 -WitnessDirectory C:\FSW_DAG01