SQL> select group#,status from v$log;
    GROUP# STATUS
---------- ----------------
         4 INACTIVE
         5 CURRENT
         6 INACTIVE
然后执行了下列语句：

ALTER DATABASE ADD LOGFILE ('/arch/redo/redo7.log') size 1024M;
ALTER DATABASE ADD LOGFILE ('/arch/redo/redo8.log') size 1024M;
ALTER DATABASE ADD LOGFILE ('/arch/redo/redo9.log') size 1024M;
ALTER DATABASE ADD LOGFILE ('/arch/redo/redo10.log') size 1024M;
ALTER DATABASE ADD LOGFILE ('/arch/redo/redo11.log') size 1024M;
ALTER DATABASE ADD LOGFILE ('/arch/redo/redo12.log') size 1024M;

然后：

SQL> select group#,status from v$log;

    GROUP# STATUS
---------- ----------------
         1 UNUSED
         2 UNUSED
         3 UNUSED
         4 INACTIVE
         5 CURRENT
         6 INACTIVE
         7 UNUSED
         8 UNUSED
         9 UNUSED
redo 组 添加时， group#的使用原则就是 从1开始，有空着的group#就选择（就复用）
另外请注意，group#是 db级别的id号，不是 instance级别的id号。

这一点跟datafile 的管理是不同的：datafile的 号是不重用的。