Versions applicable : 11.2.0.4 and higher
RMAN retention policies allow you to specify how long you want to retain backups in the backup media.
RMAN> CONFIGURE RETENTION POLICY TO REDUNDANCY 2;
The above configuration means RMAN will retain maximum of two backup copies (Versions) irrespective of time period.
When a third copy is created , the 'first' oldest copy is made obsolete and made eligible for deletion.
Following is a statement from a book titled 'Oracle RMAN for Absolute beginners' (2014) by Darl Kuhn
" I find that a retention policy based on redundancy is easier to work with and more predictable with regard to how long backups are retained. If I set redundancy to 2, I know that RMAN won’t mark as obsolete the latest two backups. In contrast, the recovery window retention policy depends on the frequency of the backups and the window length to determine whether a backup is obsolete. "
Darl seems to prefer Redundancy over Recovery Window retention policy . But, I would like to know when exactly is it suitable to use 'Redundancy' retention policy ?
Is it when you have less space available in the backup media ? Or something to do with incremental backup types (Differential/Cumulative) which is used in conjunction ?