Making Backups with RMAN - RMAN Recipes for Oracle Database 12c - page 190

All three of the previous three commands will back up all recovery files on disk, whether they're part of the fast
recovery area or are stored elsewhere on disk.

How It Works
Recovery files include full and incremental backup sets, control file auto backups, archived redo logs, and data file
copies. Recovery files do not include files such as flashback logs, the current control file, and the online redo log files.
If the fast recovery area isn't currently enabled, RMAN will back up eligible recovery files from previously configured
and enabled fast recovery area destinations.
When RMAN is backing up the fast recovery area, it has the capability to fail over to alternate archiving
destinations if necessary. For example, if an archived redo log in the fast recovery area is missing or corrupted, RMAN
will instead back up a good archived redo log from the alternative location.
It's important to remember that you must specify a tape device when backing up any fast recovery area files.
By default, RMAN turns backup optimization on during a fast recovery area backup, even if that feature is currently
turned off. You may, however, override this behavior by adding the force option when configuring backup
optimization.

Performing Incremental Backups
Problem
Instead of making a complete backup of your database every night, you want to be able to back up only the changed
data in order to complete backups within the time interval provided by your backup window and also to save
storage space.

Solution
An incremental backup includes only changed data blocks instead of entire data files, as normal full backups do.
You can make two types of incremental backups with RMAN— differential incremental backups and cumulative
incremental backups —and both of these types are explained in the following sections.

■ Note if you don't specify either the full or the incremental option during a backup, RMAN will perform a full backup

by default.

Differential Incremental Backups
A differential incremental backup is an incremental backup of all data blocks that changed subsequently to a level 0 or
a level 1 backup. RMAN first looks for a level 1 backup and, in its absence, looks for a level 0 backup and backs up all
changes since that level 0 backup. Here's an example of a differential incremental level 0 backup:

RMAN> backup incremental level 0 database;

Incremental level 0 backups can be made as image copies or backup sets.
Here's how you would perform a level 1 differential incremental backup that backs up the data blocks changed
since the most recent level 0 or, if there's no level 0 backup, a level 1 backup:

RMAN> backup incremental level 1 database;