1.SYS@ORCL>select GROUP#  ,BYTES/1024/1024 size_M,STATUS,ARCHIVED from v$log;

    GROUP#    SIZE_M STATUS          ARC                                     
 ---------- ---------- ---------------- ---                                     
          1        50 INACTIVE        YES                                     
          2        50 INACTIVE        YES                                     
          3        50 CURRENT          NO          

2.删除原有的日志组；（只操作状态为inactive的日志组）
  若要操作日志组为current时，需先进行日志切换：alter system switch logfile;
  若为active时，则可强制进行检查点：alter system checkpoint;

SYS@ORCL>alter system switch logfile;

System altered.

SYS@ORCL>alter system checkpoint; --强制执行检查点

SYS@ORCL>select GROUP#  ,BYTES/1024/1024 size_M,STATUS,ARCHIVED from v$log;

    GROUP#    SIZE_M STATUS          ARC                                     
 ---------- ---------- ---------------- ---                                     
          1        50 INACTIVE        YES                                     
          2        50 INACTIVE        YES                                     
          3        50 ACTIVE          YES    

SYS@ORCL>alter database drop logfile group 1;

Database altered.

SYS@ORCL>alter database drop logfile group 2;

Database altered.
                                

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删除后还需要去指定目录删除日志文件，后才能建立文件，如制定别的名字的日志组，应该没有此限制。
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3.添加3组大小为200M的日志组；
SYS@ORCL>alter database add logfile group 1 '/u01/app/oracle/oradata/orcl11g/redo01.log'size 200m;

Database altered.

SYS@ORCL>alter database add logfile group 2 '/u01/app/oracle/oradata/orcl11g/redo02.log'size 200m;

Database altered.

SYS@ORCL>alter database add logfile group 3 '/u01/app/oracle/oradata/orcl11g/redo03.log'size 200m;

4.给日志组添加成员
cd  /u01/app/oracle/oradata/orcl11g/
mkdir redo_bak

SYS@ORCL>alter database add logfile member '/u01/app/oracle/oradata/orcl11g/redo_bak/redo01_b.log' to group 1;
Database altered.
SYS@ORCL>alter database add logfile member '/u01/app/oracle/oradata/orcl11g/redo_bak/redo02_b.log' to group 2;
Database altered.
SYS@ORCL>alter database add logfile member '/u01/app/oracle/oradata/orcl11g/redo_bak/redo03_b.log' to group 3;
Database altered.

5.删除日志组成员

alter database drop logfile member '/u01/app/oracle/oradata/orcl11g/redo_bak/redo02_b.log';