Oracle 数据库安装之后，重做日志默认为 3组，如果需要新增删除，可以通过以下方式！

查询：

set line222
col member for a60
select a.group#,b.member member,a.bytes/1024/1024 "size(M)" from v$log a,v$logfile b where a.group#=b.group#;

新增：

单机数据库：

alter database add logfile group 4 '/oradata/orcl/redo04.log' size 50M;
alter database add logfile group 5 '/oradata/orcl/redo05.log' size 50M;
alter database add logfile group 16 '/oradata/orcl/redo16.log' size 1024M;
alter database add logfile group 17 '/oradata/orcl/redo17.log' size 1024M;
alter database add logfile group 18 '/oradata/orcl/redo18.log' size 1024M;

RAC集群数据库：

alter database add logfile thread 1 
group 4 '/oradata/orcl/redo04.log' size 50M,
group 5 '/oradata/orcl/redo05.log' size 50M,
group 6 '/oradata/orcl/redo06.log' size 50M;

alter database add logfile thread 2
group 7 '/oradata/orcl/redo07.log' size 50M,
group 8 '/oradata/orcl/redo08.log' size 50M,
group 9 '/oradata/orcl/redo09.log' size 50M;

删除：

alter database drop logfile group 16; 
alter database drop logfile group 17; 
alter database drop logfile group 18;