RMAN Incremental Backups【每日一译】--20121116

RMAN incremental backups back up only datafile blocks that have changed since a
specified previous backup. You can make incremental backups of databases,

individual tablespaces or datafiles.

RMAN的增量备份仅备份从之前指定的备份开始的数据有改变的数据块。你可以对一个数据库

独立的表空间或数据文件进行增量备份。

The goal of an incremental backup is to back up only those data blocks that have

changed since a previous backup.

增量备份的目标是仅备份那些从上次备份开始的已经发生改变的数据块。

The primary reasons for making incremental backups part of your strategy are:
■ For use in a strategy based on incrementally updated backups, where these
incremental backups are used to periodically roll forward an image copy of the
database
■ To reduce the amount of time needed for daily backups
■ To save network bandwidth when backing up over a network
■ To get adequate backup performance when the aggregate tape bandwidth
available for tape write I/Os is much less than the aggregate disk bandwidth for

disk read I/Os

将增量备份作为你备份策略的一部份的主要理由：

#对于基于增量更新备份的策略，这些增量备份是用于周期性的作为数据库的一个前滚的镜

像备份。

#减少每日备份所需的时间

#节省网络带宽当备份通过网络进行时

#去获取足够的备份性能当总的磁带可用带宽在写IO方面远远少于总的磁盘带宽在读IO方面。

■ To be able to recover changes to objects created with the NOLOGGING option. For
example, direct load inserts do not create redo log entries and their changes cannot
be reproduced with media recovery. They do, however, change data blocks and so

are captured by incremental backups.

#可以还原那些带有NOLOGGING选项的创建对象。比如直接插入不创建REDO日志的条目，并且

它们是不可以通过介质还原重现的。它们能做的是将改变的数据块捕获用于增量备份。

■ To reduce backup sizes for NOARCHIVELOG databases. Instead of making a whole

database backup every time, you can make incremental backups.

#减少了NOARCHIVELOG模式的数据库的大小。代替每次都做全库的备份，你可以使用增

量备份。

As with full backups, if you are in ARCHIVELOG mode, you can make incremental
backups if the database is open; if the database is in NOARCHIVELOG mode, then

you can only make incremental backups after a consistent shutdown.

对于使用全备份，如果是在归档模式，你可以在数据库在打开的状态进行增量备份，如果

数据库属于非归档模式，那么你仅能在一致性的关闭库后使用增量备份。

One effective strategy is to make incremental backups to disk, and then back up the
resulting backup sets to a media manager with BACKUP AS BACKUPSET. The
incremental backups are generally smaller than full backups, which limits the space
required to store them until they are moved to tape. Then, when the incremental
backups on disk are backed up to tape, it is more likely that tape streaming can be
sustained because all blocks of the incremental backup are copied to tape. There is no
possibility of delay due to time required for RMAN to locate changed blocks in the

datafiles.

一个有效的策略去将增量备份到磁盘中，然后将备份集的结果备份到介质管理器使用“BACKUP AS BACKUPSET”

增量备份一般来说是小于全备份的，它线束了需要存储的空间直到它们被移到磁带之前。然后

当在磁盘上的增量备份备份到磁带时，它更可能那样磁带流动可以被持续因为所有的增量备份块是被COPY到磁带。

不存在因为RMAN需要时间去定位改变数据块在数据文件中的延迟。