1.最大保护模式配置。
1.1确认是否有standby log。

SQL> SELECT * FROM V$LOGFILE WHERE TYPE = 'STANDBY';
 
no rows selected

1.2停止recover进程。
SQL> alter database recover managed standby database cancel;
 
Database altered.

1.3在standby数据库上，创建standby log，大小要与primary端的redo一致。

SQL> ALTER DATABASE ADD STANDBY LOGFILE group 4
 ('/oracle/oradata/prod/log4a.rdo','/oracle/oradata/prod/log4b.rdo') SIZE 15728640;

SQL> ALTER DATABASE ADD STANDBY LOGFILE group 6
 ('/oracle/oradata/prod/log6a.rdo','/oracle/oradata/prod/log6b.rdo') SIZE 15728640;

1.4在primary端修改日志同步模式

SQL> alter system set log_archive_dest_2='SERVICE=stdby LGWR SYNC AFFIRM' scope=both;
 
System altered.

1.5启用最大保护模式

SQL> ALTER DATABASE SET STANDBY DATABASE TO MAXIMIZE PROTECTION;

 
Database altered.

1.6查询standby redo是否被激活

SQL> SELECT GROUP#,THREAD#,SEQUENCE#,ARCHIVED,STATUS FROM V$STANDBY_LOG;
 
    GROUP#    THREAD#  SEQUENCE# ARC STATUS
---------- ---------- ---------- --- ----------
         4          1         25 YES ACTIVE
         5          0          0 YES UNASSIGNED
         6          0          0 YES UNASSIGNED

在standby端的告警日志里，可以看到：
Fri May 23 16:10:35 2008
ARC1: Evaluating archive   log 4 thread 1 sequence 25
ARC1: Beginning to archive log 4 thread 1 sequence 25
Creating archive destination LOG_ARCHIVE_DEST_1: '/oracle/arch/1_25.dbf'
Fri May 23 16:10:35 2008
RFS: Successfully opened standby logfile 5: '/oracle/oradata/stdby/log5a.rdo'
Fri May 23 16:10:36 2008
ARC1: Completed archiving  log 4 thread 1 sequence 25
Fri May 23 16:10:42 2008
Media Recovery Log /oracle/arch/1_25.dbf
Media Recovery Waiting for thread 1 seq# 26 (in transit)

1.7故障测试。
standby数据库没有启动的情况下，尝试打开primary数据库，出现如下错误：

ALTER DATABASE OPEN
Fri May 23 16:20:06 2008
LGWR: Primary database is in CLUSTER CONSISTENT mode
LGWR: Primary database is in MAXIMUM PROTECTION mode
LGWR: Destination LOG_ARCHIVE_DEST_1 is not serviced by LGWR
LNS0 started with pid=12
Fri May 23 16:20:10 2008
LGWR: Error 1034 verifying archivelog destination LOG_ARCHIVE_DEST_2
LGWR: Continuing...
Fri May 23 16:20:10 2008
Errors in file /oracle/admin/prod/bdump/prod_lgwr_1431.trc:
ORA-01034: ORACLE not available
LGWR: Error 1034 disconnecting from destination LOG_ARCHIVE_DEST_2 standby host 'stdby'
LGWR: Minimum of 1 applicable standby database required
Fri May 23 16:20:10 2008
Errors in file /oracle/admin/prod/bdump/prod_lgwr_1431.trc:
ORA-16072: a minimum of one standby database destination is required
LGWR: terminating instance due to error 16072
Instance terminated by LGWR, pid = 1431

可见，这种情况下，实例被停止，原因是lgwr进程无法正常工作。