Recovery Window-Based Retention VS Redundancy-Based Retention

Question

Hi Experts,
We'd like to know your take on the use of Recovery Window-Based Retention Policy e.g.
RMAN> CONFIGURE RETENTION POLICY TO RECOVERY WINDOW OF 7 DAYS;against the use of Redundancy-Based Retention Policy, e.g.
CONFIGURE RETENTION POLICY TO REDUNDANCY 7;Do you have any recommendations or preferences to which should be used? Is there a preferred method by oracle?
We're currently setting up RMAN for a client that's using Oracle 11.1.0.7 standard edition, so is there a preference to what's better suited for the standard edition? The plan is to back up data to Disk, and this data will be then backed up to tape.
Thanks

Answer 1

REDUNDANCY 7 is 7 backups -- irrespective of the number of days.
If you are running only 1 backup a day, you'd assume that it is equivalent to 7 days. However, if one day you run a backup twice, then the 7-day old backup becomes redundant ! If, the next day, you again run the backup twice, the 5-day old backup becomes redundant ! (Conversely, if you don't run a backup for 2 days, then even the 9 day old backup is not redundant !).
So, be aware (or beware) that any adhoc backup runs or changes to the backup frequency would change your retention duration (and if this happens 6 months from now, the IT Manager / DBA onsite may not know that retention has changed !)
Hemant K Chitae