RMAN Backup Strategies 

Use

The decision whether to use the Recovery Manager or not, and which backup library to use with it, depends largely on the strategy that you use to back up your data The best strategy depends on the size of the database, the amount of data added or changed each day, the backup media you use and your security requirements.

Normal Backups

Normal backups, that is complete or partial backups of the database ( backup_mode = all|<object_list> ), were previously made with BRBACKUP or with an external backup tool and the BACKINT interface. As of Release 4.5A you can also make these backups with the Recovery Manager. The advantages of the RMAN include automatic recognition of database block errors, a lower backup volume and fewer redo logs.

You can make RMAN backups without a backup library to a local disk only. The Oracle server process takes care of the entire backup to disk. The data on the disk is a one-to-one copy of the database files. You cannot use RMAN to make a normal backup to a remote disk. If you want to make RMAN backups to tape devices, you need a backup library for tape management purposes.

Incremental Backups with RMAN.

As of Release 4.5A, BRBACKUP supports incremental backups of the database (RMAN). The Oracle Recovery Manager offers different types of incremental backups (different levels, cumulative or non-cumulative). The integration of RMAN into BRBACKUP is limited to cumulative incremental backups of level 1. This means that in the event of a recovery you only need to import one incremental backup. In an incremental backup, only the changes that have been made since the last complete backup are saved. This significantly reduces the amount of data that has to be backed up. This strategy is particularly useful for large databases.

An incremental backup requires an earlier reference backup, a complete backup of the database (level 0). RMAN backs up all Oracle database blocks that have already been used. The subsequent incremental backup (level 1) of the database backs up all Oracle database blocks that have changed since the last complete backup (level 0). This takes into account all changes that have been made to the database.

You can only make incremental backups (level 1) with RMAN. When you make the complete backup (level 0) you also have the option of using BRBACKUP or an external backup tool and BACKINT. BRBACKUP automatically logs the backup as a level 0 backup.

An RMAN backup has to read the database to see if a block has been used or changed just as many times as a backup without RMAN. This means that an incremental backup may not reduce backup time. A significant reduction in backup time is achieved only if the speed of the tape devices is the reason for slow backups.

For security when using an incremental backup strategy, choose a sufficiently long expiration period for the tapes (at least 28 days), so that you always have several complete backups available. Make sure the offline redo log files cover the period up to the oldest complete backup, and that they are backed up daily.

Features

Full backup (full, level 0)

Incremental backup (Incr, level 1)

Activities

The following describes a possible incremental backup scenario:

The tools used to implement this backup strategy depend on the specific requirements of the end user regarding backup media, volume of data and so on.

For more information on incremental backups, refer to the relevant Oracle8 documentation.