若要發出 ALTER DATABASE SET WITNESS，全部三個伺服器執行個體必須互連，而且鏡像資料庫必須跟上。等到這些條件都滿足之後，再重新發出命令。

To issue ALTER DATABASE SET WITNESS, all three server instances must be interconnected, and the mirror database must be caught up. When these conditions are met, reissue the command.