A full backup contains all used data file blocks
A level 0 incremental backup is equivalent to a full backup that has been marked as level 0
A cumulative level 1 incremental backup contains only blocks modified since the last level 0 incremental backup.
A differential level 1 incremental backup contains only blocks modified since the last incremental backup.
Full Backups
A full backup is different from a whole database backup. A full data file backup is a backup that includes every used data block in the file. RMAN copies all blocks into the backup set or image copy, skipping only those data file blocks that are not part of an existing segment. For a full image copy, the entire file contents are reproduced exactly. A full backup cannot be part of an incremental backup strategy; it cannot be the parent for a subsequent incremental backup.
Incremental Backups
An incremental backup is either a level 0 backup, which includes every block in the data files except blocks that have never been used, or a level 1 backup, which includes only those blocks that have been changed since a previous backup was taken. A level 0 incremental backup is physically identical to a full backup. The only difference is that the level 0 backup (as well as an image copy) can be used as the base for a level 1 backup, but a full backup can never be used as the base for a level 1 backup.
Incremental backups are specified by using the INCREMENTAL keyword of the BACKUP command. You specify INCREMENTAL LEVEL [0 | 1].
RMAN can create multilevel incremental backups as follows:
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Differential: Is the default type of incremental backup that backs up all blocks changed after the most recent incremental backup at either level 1 or level 0
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Cumulative: Backs up all blocks changed after the most recent backup at level 0
Examples
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To perform an incremental backup at level 0, use the following command:
RMAN> BACKUP INCREMENTAL LEVEL 0 DATABASE;
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To perform a differential incremental backup, use the following command:
RMAN> BACKUP INCREMENTAL LEVEL 1 DATABASE;
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To perform a cumulative incremental backup, use the following command:
RMAN> BACKUP INCREMENTAL LEVEL 1 CUMULATIVE DATABASE;
RMAN makes full backups by default if neither FULL nor INCREMENTAL is specified. Unused block compression causes never-written blocks to be skipped when backing up data files to backup sets, even for full backups.
A full backup has no effect on subsequent incremental backups, and is not considered part of any incremental backup strategy, although a full image copy backup can be incrementally updated by applying incremental backups with the RECOVER command.
