In order to proceed with the best backup strategy in RMAN, it is necessary to know some concepts about the types of Backups.
BACKUP FULL: It is the copy of all Datafiles and Blocks used, but this strategy cannot be used with INCREMENTAL backups.
INCREMENTAL BACKUP LEVEL 0: It is a Backup similar to BACKUP FULL but is included in an incremental strategy. With this we can say that the Incremental Backup of level 0 is a Full Backup that becomes the BASE of all other incremental backups whose level is greater than 0.
There are two types of level 1 incremental backups:
DIFFERENTIAL INCREMENTAL BACKUP: Backs up all changed blocks after the most recent incremental backup at level 1 or 0;
CUMULATIVE INCREMENTAL BACKUP: Backs up all changed blocks after the most recent incremental backup at level 0.
Let's look at the strategy of the DIFFERENTIAL INCREMENTAL BACKUP
The image above shows the activities of a Backup with a strategy defined as Differential Incremental Backups.
On Sunday the Backup was made INCREMENTAL OF LEVEL 0 he used all the blocks of the Database.
For the rest of the week (Monday to Saturday), the LEVEL 1 DIFFERENTIAL INCREMENTAL BACKUP copied all the blocks that have changed since the most recent incremental backup of level 1 or 0.
Advantage: This type of strategy models costs very little media space, by only copying the blocks changing of day up to Level 0 throughout the week.
Disadvantage: More attention, in case one of the backups during the strategy fails, it is necessary to have all the pieces of the LEVEL 1 Backup to recover your Database.
You have a Level 0 and Level 1 Backup strategy throughout the week, but on Wednesday you didn't realize that there was a LEVEL 1 failure and the Database needs to be restored by Saturday. The backups will only guarantee their recovery until Tuesday where there was no failure.
Let's look at the strategy of the CUMULATIVE INCREMENTAL BACKUP
LEVEL 1 CUMULATIVE BACKUP: It copies all the changed and used blocks since the existence of Level 0 Incremental Backup. This process ensures that you only need an Incremental Backup of any specific level.
Advantage: Reduces the complexity of the restore operation where you only need any level.
Disadvantage: Demanding more space on Disk, it also requires more time in the execution of backups because it is about making a copy of previous backups at the same level.