Explanation/Reference:
Explanation:
Configuring a Redundancy-Based Retention Policy
The REDUNDANCY parameter of the CONFIGURE RETENTION POLICY command specifies how many full or level 0 backups of each data file and control file that RMAN should keep. If the number of full or level
0backups for a specific data file or control file exceeds the REDUNDANCY setting, then RMAN considers the extra backups as obsolete. The default retention policy is REDUNDANCY 1.
As you produce more backups, RMAN keeps track of which ones to retain and which are obsolete. RMAN retains all archived logs and incremental backups that are needed to recover the non obsolete backups.
Assume that you make a full backup of data file 7 on Monday, Tuesday, Wednesday, and Thursday. You now have four full backups of this data file. If REDUNDANCY is 2, then the Monday and Tuesday backups are obsolete. If you make another backup on Friday, then the Wednesday backup of data file 7 becomes obsolete. Assume a different case in which REDUNDANCY is 1. You run a level 0 database backup at noon on Monday, a level 1 cumulative backup at noon on Tuesday and Wednesday, and a level 0 backup at noon on Thursday. Immediately after each daily backup you run the command DELETE OBSOLETE.
The Wednesday DELETE command does not remove the Tuesday level 1 backup because this backup is not redundant: the Tuesday level 1 backup could be used to recover the Monday level 0 backup to a time between noon on Tuesday and noon on Wednesday. However, the DELETE command on Thursday removes the previous level 0 and level 1backups.
Run the CONFIGURE RETENTION POLICY command at the RMAN prompt, as in the following example:
CONFIGURE RETENTION POLICY TO REDUNDANCY 3;