When PFM - RM for Microsoft SQL Server monitors the databases in the mirroring configuration, PFM - RM for Microsoft SQL Server collects the performance information from the databases other than the mirror databases (such as the principal database and the database(s) in the non-mirroring configuration).
The following figure summarizes how PFM - RM for Microsoft SQL Server monitors the database in the mirroring configuration:
Figure 2-5 Overview of how PFM - RM for Microsoft SQL Server monitors the database in the mirroring configuration