When you are taking backups regularly to a specified disk then after some period of time the backup disk will get full and you will need to delete old backups to make space for new backups.
Usually you delete the old backups manually by following a particular rule like, deleting all the backups taken before 1 month or keep 2 backup copies of datafiles and delete older copies.
Manually identifying and deleting old backup files is cumbersome. To help you out, Oracle RMAN has a feature called RETENTION POLICY.
By configuring Retention Policy in RMAN, you can easily delete old backups by just giving one command.
Let's see how to configure Retention Policy and how to delete old backups
You can configure retention policy to either number of days or number of copies. By default the RETENTION POLICY is set to redundancy 1.
RMAN> configure retention policy to redundancy 2;
In the above command we are asking RMAN to keep 2 backup copies of each file. Backup copies which are older than 2 copies can be marked as obsolete and hence can be deleted.
RMAN> configure retention policy to recovery window of 15 days;
When we issue this command RMAN will mark obsolete those backups which are older than 15 days.
To view backups which have become obsolete according to the current retention policy you can give the following command
RMAN> report obsolete;
We can delete obsolete backups by giving the following command
RMAN> delete obsolete;
Once retention policy is configured we can anytime issue the above command to delete old backups and free up space.
Type the following command to know the currently configured RETENTION POLICY
RMAN> show retention policy;
Resetting RETENTION POLICY to default
You can reset the RETENTION POLICY to default value by giving the following command
RMAN> configure retention policy clear;
Disabling RETENTION POLICY
You can also disable retention policy. Disabling makes RMAN not consider any backup as obsolete