1、环境描述
11g RAC+ADG 最大可用模式

2、异机恢复
告警日志报错如下：
ORA-16072: a minimum of one standby database destination is required
Instance terminated by LGWR
然后实例异常终止

3、原因
Although you removed all configuration files, removed the Standby Database,
and reset all LOG_ARCHIVE_DEST_n-Parameters, the Primary Database has still
the Protection Mode stored in the Data Dictionary. The Protection Mode
requires a running connection to a Standby Database with LGWR SYNC as
Log-Transportation Mode. Since the standby is not available anymore,
LGWR of the primary terminates the instance.

4、处理方法

Startup the Primary Database in Mount State and set the Protection Mode back
to Maximum Performance Mode, which is the Default:
--数据库mount状态下，执行如下命令，然后重启数据库
SQL> ALTER DATABASE SET STANDBY DATABASE TO MAXIMIZE PERFORMANCE;

Then shutdown the Database and restart again.