一：在制定rman备份策略前，需对redo日志进行评估。本文按照官方文档的建议进行设置：

文档建议：

Oracle recommends that you multiplex the online redo log. The loss of log files can be catastrophic if recovery is required. When you multiplex the online redo log, the database must increase the amount of I/O it performs. Depending on your system, this additional I/O may impact overall database performance.

oracle建议使用多个redolog（如图中redo01a.log），保证redo的冗余！，并将冗余的redolog放在不同的磁盘上（图中redo01a.log放在diakA中），以减少I/O开销！

二：归档日志的配置本文参考的是：

To archive to multiple destinations, you can choose to archive to two or more locations using theLOG_ARCHIVE_DEST_n initialization parameters, or to archive only to a primary and secondary destination using theLOG_ARCHIVE_DEST and LOG_ARCHIVE_DUPLEX_DEST initialization parameters.

oracle还是建议使用log_archive_dest_n来配置archivelog的放置路径！而且还是遵循上的冗余策略！

注意：

If you configure a Fast Recovery Area (by setting the DB_RECOVERY_FILE_DEST andDB_RECOVERY_FILE_DEST_SIZE parameters) and do not specify any local archive destinations, the database automatically selects the Fast Recovery Area as a local archive destination and setsLOG_ARCHIVE_DEST_1 to USE_DB_RECOVERY_FILE_DEST.

如果指定了 快速恢复区（Fast Recovery Area），并且没有指定任何本地归档路径时。oracle将默认快速恢复区作为归档路径。

You must ensure that there is sufficient disk space at all times for archive log destinations. If the database encounters a disk full error as it attempts to archive a log file, a fatal error occurs and the database stops responding. You can check the alert log for a disk full message.

要确保指定的归档路径有足够的空间来存放归档日志。如果oracle在归档时发现空间不足的话，就会停止响应（挂起），在alter文件中会有提示磁盘不足的消息！

三：所以快速恢复区的大小需要dba进行估算后设置! 

Use of the fast recovery area is strongly recommended. Consider configuring a fast recovery area as a first step in implementing a backup strategy
oracle强烈推荐使用快速恢复区。制定备份策略的第一步就是配置快速恢复区！

You enable the fast recovery area by setting two initialization parameters. 
These parameters enable the fast recovery area without having to shut down and restart the database instance.

启用fast recovery area只需启用以下2个参数就OK了！不用重启instance

You set the size of the fast recovery area with the parameter DB_RECOVERY_FILE_DEST_SIZE first, 
and then you set the physical location of the flash recovery files with the parameter DB_RECOVERY_FILE_DEST.

以下为官网上如何配置快速恢复区的大小：

The larger the fast recovery area is, the more useful it becomes. Ideally, the fast recovery area should be large enough to contain the files listed in Table 5-2. The recovery area should be able to contain a copy of all datafiles in the database and the incremental backups used by your chosen backup strategy.

If providing this much space is impractical, then it is best to create an area large enough to keep a backup of the most important tablespaces and all the archived logs not yet on tape. At an absolute minimum, the fast recovery area must be large enough to contain the archived redo logs not yet on tape. If the recovery area has insufficient space to store new flashback logs and meet other backup retention requirements, then to make room, the recovery area may de