> RMAN has the ability to detect which blocks in a datafile have changed since the last backup and will copy only those modified blocks.
> Skipping unmodified blocks gives RMAN a big advantage over file-based backups in that the resources required to do a backup or restore can be considerably less.
> Much of the nomenclature around incremental backups contains the term level. The basic idea behind RMAN level-based backups is to back up only blocks that have been modified since the previous backup.
> Incremental backups can be applied to the database, tablespaces, or datafiles.
> These levels can range from level 0 to a maximum of level 4.
> There are two flavors of incremental backups --
1) Differential
2) Cumulative
1) Differential incremental Backup
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> To back up blocks that have changed since level n or lower
> For example, if you take a level 1 differential backup, you will back up blocks that have changed since the previous level 1 backup.
Note
Differential backups are the default incremental backup mode.
If you take an incremental backup higher than level 0, and no prior level 0 exists, RMAN automatically creates a level 0 backup.
2) Cumulative incremental backup
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A cumulative incremental backup instructs RMAN to back up blocks that have changed since level n-1 or lower.
For example, if you take a level 1 cumulative backup, RMAN will back up blocks that have changed since the most recent level 0 backup.
A differential backup takes less space and time to perform but requires more time to restore. It follows that a cumulative backup takes more space and time to perform but less time to restore. So it becomes a tradeoff issue; do you want to minimize your backup time or minimize your restore time? We prefer to minimize our restore time, and therefore, we use cumulative backups. For small databases, we recommend daily RMAN level 0 backups.
For example: Here we tell RMAN to back up all blocks that have been modified since the most recent level 3 or lower backup :
RMAN> backup incremental level 4 cumulative database;