In this model, shown in Figure 17.1, SQL mirroring is used solely to create a backup copy of the SharePoint databases so that they can be used to failover the environment in the event of a problem on the principal SQL server. Because synchronous DB mirroring is used, all SharePoint databases (excluding a few services databases that cannot be mirrored; more on this later) can be mirrored from the principal server to another.
Figure 17.1. Examining the single-site synchronous mirroring farm example.
This model requires two distinct SQL instances, and uses a SQL witness server to fail over from the principal to the mirror databases in the event of a failure. Because all SharePoint servers are in the same data center, there are only two SharePoint Web/Query/Service App servers in the farm.