Oracle 9204 版本。
SQLPLUS SYSTEM/MANAGER

SQL> select group# from v$log;

GROUP#
----------
1
2
3

创建日志文件组4,5
---------------------------
SQL> alter database add logfile group 4 '/opt/oracle/product/9i/oradata/oracle9i/redo04.log' size 200M;

Database altered.

SQL> alter database add logfile group 5 '/opt/oracle/product/9i/oradata/oracle9i/redo05.log' size 200M;

Database altered.

将日志文件组切换到新建立的4,5日志文件组上
--------------------------------------------------------------
SQL> alter system switch logfile;

System altered.

SQL> alter system switch logfile;

System altered.

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

GROUP# STATUS
---------- ----------------
1 INACTIVE
2 INACTIVE
3 INACTIVE
4 INACTIVE
5 CURRENT[@more@]删除已有的1,2,3日志文件组
---------------------------------------
SQL> alter database drop logfile group 1;

Database altered.

SQL> alter database drop logfile group 2;

Database altered.

SQL> alter database drop logfile group 3;

Database altered.

增加新的日志文件1,2,3，并设定容量为200M
------------------------------------------------------------
SQL> alter database add logfile group 1 '/opt/oracle/product/9i/oradata/oracle9i/redo01.log' size 200M;

Database altered.

SQL> alter database add logfile group 2 '/opt/oracle/product/9i/oradata/oracle9i/redo02.log' size 200M;

Database altered.

SQL> alter database add logfile group 3 '/opt/oracle/product/9i/oradata/oracle9i/redo03.log' size 200M;

Database altered.

SQL> alter system switch logfile;

System altered.

SQL> alter system switch logfile;

System altered.

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

GROUP# STATUS
---------- ----------------
1 INACTIVE
2 CURRENT
3 UNUSED
4 INACTIVE
5 INACTIVE

删除刚刚增加的日志文件组4,5
-----------------------------------------
SQL> alter database drop logfile group 4;

Database altered.

SQL> alter database drop logfile group 5;

Database altered.

注意：每一步drop操作，都需要手工删除os中的物理文件。