Choosing the AD FS Database Platform

After it is determined how many servers will be needed, the next important consideration is the database platform. The configuration data for AD FS is stored in the AD FS configuration database. For database platforms, AD FS 2.0 supports either a full installation of SQL Server (2005 or newer) or the Windows Internal Database (WID) feature that is included with Windows Server 2008 and Windows Server 2008 R2. From a performance perspective, there is not much difference between the two database platforms, and the AD FS functionality is also nearly equal between the two.

For use with Office 365 or Lync Online, Microsoft recommends using the WID database platform for the AD FS topology, because this provides data resiliency, is simple to deploy, and also saves on licensing costs compared to SQL. When the first federation server is installed, this server becomes the primary federation server, and a read/write copy of the configuration database based on WID is installed locally. Any additional federation servers added to the farm are secondary federation servers, and replicate changes to the configuration database from the primary federation server to a local read-only copy.