Database Reference
In-Depth Information
Creating Incremental Backups
RMAN has three separate and distinct incremental backup features:
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Incremental-level backups
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Incrementally updating backups
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Block change tracking
With incremental-level backups, RMAN only backs up the blocks that have been modified since a previous
backup. Incremental backups can be applied to the entire database, tablespaces, or data files. Incremental-level
backups are the most commonly used incremental feature with RMAN.
Incrementally updating backups is a separate feature from incremental-level backups. These backups take image
copies of the data files and then use incremental backups to update the image copies. This gives you an efficient way
to implement and maintain image copies as part of your backup strategy. You only take the image copy backup once,
and then use incremental backups to keep the image copies updated with the most recent transactions.
Block change tracking is another feature designed to speed up the performance of incremental backups. The idea
here is that an OS file is used to record which blocks have changed since the last backup. RMAN can use the block
change tracking file to quickly identify which blocks need to be backed up when performing incremental backups.
This feature can greatly improve the performance of incremental backups.
Taking Incremental-Level Backups
RMAN implements incremental backups through levels. Starting with Oracle 10g, there are only two documented
levels of incremental backups: level 0 and level 1. Prior versions of Oracle offer five levels, 0-4. These levels (0-4) are
still available but are not specified in the Oracle documentation. You must first take a level 0 incremental backup to
establish a baseline, after which you can take a level 1 incremental backup.
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a full backup backs up the same blocks as a level 0 backup. however, you can't use a full backup with
incremental backups. Furthermore, you have to start an incremental backup strategy with a level 0 backup. if you attempt
to take a level 1 backup, and no level 0 exists, rMaN will automatically take a level 0 backup.
Note
Here is an example of taking an incremental level 0 backup:
RMAN> backup incremental level=0 database;
Suppose for the next several backups you want to back up only the blocks that have changed since the last
incremental backup. This line of code takes a level 1 backup:
RMAN> backup incremental level=1 database;
There are two different types of incremental backups: differential and cumulative. Which type you use depends
on your requirements. Differential backups (the default) are smaller but take more time to recover from. Cumulative
backups are larger than differential backups but require less recovery time.
A differential incremental level 1 backup instructs RMAN to back up blocks that have changed since the last
level 1 or level 0 backup, whereas a cumulative incremental level 1 backup instructs RMAN to back up blocks that
have changed since the last level 0 backup. Cumulative incremental backups, in effect, ignore any level 1 incremental
backups.
