SQLServer2012镜像主库挂掉如何切换到镜像备库

主节点的主库服务挂了，无法启动。强行启动从库。 在备库执行： USE master;   ALTER DATABASE ec SET PARTNER FORCE_SERVICE_ALLOW_DATA_LOSS;之后会恢复两分钟，备机的数据库就能用了。 数据库日志： The mirrored database "ec" is changing roles from "MIRROR" to "PRINCIPAL" because the mirroring session or availability group failed over due to FORCE_SERVICE_ALLOW_DATA_LOSS. This is an informational message only. No user action is required.Starting up database 'ec'.1 transactions rolled forward in database 'ec' (7:0). This is an informational message only. No user action is required.0 transactions rolled back in database 'ec' (7:0). This is an informational message only. No user action is required.CHECKDB for database 'ec' finished without errors on 2016-09-01 15:33:43.907 (local time). This is an informational message only; no user action is required. 如果主机恢复了就切回去。--原来的主服务器恢复,可以继续工作,需要重新设定镜像，第一次可能会报个错在备库执行：USE master;   ALTER DATABASE ec SET PARTNER RESUME; --恢复镜像   ALTER DATABASE ec SET PARTNER FAILOVER; --切换主备 主备切换完成。