RMAN的备份保留策略

使用RMAN可以对备份集进行管理，其中的一个重要特性是备份保留策略的设置，备份保留策略是为满足备份需求而设置的备份保留原则。
备份保留策略可以基于冗余（Redundancy）或者基于恢复窗口（Recovery Window）。对于基于冗余的策略，可以定义一个数字n用于标示RMAN为每个文件保留至少n个不同的备份；在基于恢复窗口的保留策略中，需要定义一个时间长度（例如，一周或一个月），RMAN会保留足够的备份，以便在定义的时间长度内可以进行基于任何时间点的恢复。
当备份不再需要时会被标记为废弃（obsolete），但是废弃的备份不会自动删除，只是在RMAN目录中标记为丢弃，其状态依旧为available，要查看标记为丢弃的备份可以使用report obsolete命令，只有使用delete obsolete才会真正删除丢弃的备份。
通过在RMAN中执行show all命令可以看到很多参数配置，其中第一项就是冗余策略设置：

RMAN> show all;

RMAN 配置参数为:
CONFIGURE RETENTION POLICY TO REDUNDANCY 1; # default
CONFIGURE BACKUP OPTIMIZATION OFF; # default
CONFIGURE DEFAULT DEVICE TYPE TO DISK; # default
CONFIGURE CONTROLFILE AUTOBACKUP ON;
………
缺省的冗余个数设置为1，以下输出标识了一个全备份和归档备份为废弃：
RMAN> report obsolete;
RMAN 保留策略将应用于该命令
将 RMAN 保留策略设置为冗余 1
已废弃的备份和副本报表
类型                 关键字 完成时间           文件名/句柄
-------------------- ------ ------------------ --------------------
备份集               15     02-3月 -07
备份段       15     02-3月 -07         D:\BACKUP\EYGLEARCH_EYGLE_20070302_17
备份集               17     02-3月 -07
备份段       17     02-3月 -07         D:\BACKUP\EYGLEFULL_EYGLE_20070302_19

如果REDUNDANCY设置为2，则这两个备份集都将被保留：

RMAN> CONFIGURE RETENTION POLICY TO REDUNDANCY 2;

新的 RMAN 配置参数:
CONFIGURE RETENTION POLICY TO REDUNDANCY 2;
已成功存储新的 RMAN 配置参数

RMAN> report obsolete;
RMAN 保留策略将应用于该命令
将 RMAN 保留策略设置为冗余 2
未找到已废弃的备份

要删除过期备份可以使用delete obsolete命令（nopromt指定无需确认立即删除）：

RMAN> delete noprompt obsolete;

RMAN 保留策略将应用于该命令
将 RMAN 保留策略设置为冗余 1
使用通道 ORA_DISK_1
删除以下已废弃的备份和副本:
类型                 关键字 完成时间           文件名/句柄
-------------------- ------ ------------------ --------------------
备份集               15     02-3月 -07
备份段       15     02-3月 -07         D:\BACKUP\EYGLEARCH_EYGLE_20070302_17
备份集               17     02-3月 -07
备份段       17     02-3月 -07         D:\BACKUP\EYGLEFULL_EYGLE_20070302_19
已删除备份段
备份段 handle=D:\BACKUP\EYGLEARCH_EYGLE_20070302_17 recid=15 stamp=616160448
已删除备份段
备份段 handle=D:\BACKUP\EYGLEFULL_EYGLE_20070302_19 recid=17 stamp=616160536
2 对象已删除

如果要长期保留备份集，使之不受保留策略影响，则可以使用RMAN的backup … keep选项，keep until time可以指定备份集保留的时间，keep forever可以指定永远保留备份集。
以下命令用于备份指定的表空间，保留时间为365天，注意备份时会提示备份集的过期时间，在备份完成之后，相关的归档日志、控制文件、参数文件会同时备份下来：

E:\>rman target /

Recovery Manager: Release 11.2.0.2.0 - Production on Mon Jan 31 16:05:11 2011
Copyright (c) 1982, 2009, Oracle and/or its affiliates.  All rights reserved.

connected to target database: EYGLEE (DBID=3941320050)
RMAN> backup tablespace users format 'E:\backup\users%U.bk'
2> keep until time 'sysdate + 365';

Starting backup at 31-JAN-11
current log archived

using channel ORA_DISK_1
backup will be obsolete on date 31-JAN-12
archived logs required to recover from this backup will be backed up
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00004 name=E:\ORADATA\EYGLEE\O1_MF_USERS_6BD0BQBH_.DBF
channel ORA_DISK_1: starting piece 1 at 31-JAN-11
channel ORA_DISK_1: finished piece 1 at 31-JAN-11
piece handle=E:\BACKUP\USERS0IM3GKGQ_1_1.BK tag=TAG20110131T160857 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:15

using channel ORA_DISK_1
backup will be obsolete on date 31-JAN-12
archived logs required to recover from this backup will be backed up
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
including current SPFILE in backup set
channel ORA_DISK_1: starting piece 1 at 31-JAN-11
channel ORA_DISK_1: finished piece 1 at 31-JAN-11
piece handle=E:\BACKUP\USERS0JM3GKHA_1_1.BK tag=TAG20110131T160857 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01

current log archived
using channel ORA_DISK_1
backup will be obsolete on date 31-JAN-12
archived logs required to recover from this backup will be backed up
channel ORA_DISK_1: starting archived log backup set
channel ORA_DISK_1: specifying archived log(s) in backup set
input archived log thread=1 sequence=357 RECID=151 STAMP=741888557
channel ORA_DISK_1: starting piece 1 at 31-JAN-11
channel ORA_DISK_1: finished piece 1 at 31-JAN-11
piece handle=E:\BACKUP\USERS0KM3GKHE_1_1.BK tag=TAG20110131T160857 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01

using channel ORA_DISK_1
backup will be obsolete on date 31-JAN-12
archived logs required to recover from this backup will be backed up
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
including current control file in backup set
channel ORA_DISK_1: starting piece 1 at 31-JAN-11
channel ORA_DISK_1: finished piece 1 at 31-JAN-11
piece handle=E:\BACKUP\USERS0LM3GKHG_1_1.BK tag=TAG20110131T160857 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01
Finished backup at 31-JAN-11

注意，使用keep forever命令需要存在恢复目录：

RMAN> backup tablespace system format 'E:\backup\system%U.bk'
2> keep forever;

Starting backup at 31-JAN-11
current log archived

using channel ORA_DISK_1
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of backup command at 01/31/2011 16:13:52
RMAN-06522: KEEP FOREVER option is not supported without the recovery catalog