As stated here SQL mirroring is not supported for the ConfigMgr database. However a technet article do not stop all database administrors’s from enabling the setting anyway believing that it will not cause any issues – but boy it does. SQL mirroring will break the SCCM SP1 upgrade process and leave the primary site server in a non-functional mode where a site restore is the only way back.
The issue can be found in the ConfigMgrSetup.log file.
USE [cm_ps1]; ALTER DATABASE [cm_ps1] SET SINGLE_USER WITH ROLLBACK IMMEDIATE; $$<Configuration Manager Setup><01-11-2013 10:38:29.887+00><thread=4136 (0×1028)>
*** [Microsoft][SQL Server Native Client 11.0][SQL Server]The operation cannot be performed on database "cm_ps1" because it is involved in a database mirroring session.
Unfortunately the upgrade prerequisite checker do not check for mirroring