There is incorrect thought :
Setting RMAN recovery window to 14 days ==> any backup older than 14 days become obsolete. Incorrect
Regarding to Oracle document, A recovery window is a period of time that begins with the current time and extends backward in time to the point of recoverability. In other words, Recovery window determines the earliest point of time when recovery is possible.Consequently, RMAN may need backups older than recovery window=n days to recover database to n days ago.
Let me provide you an example :
- Recovery window 7 days.
- Scheduled DB backups. (Nov 1st,Nov 14th,Nov 21th,Nov 28th)
- current date : Nov 16th.
Nov 1st -- Nov 14th ---Nov 21th-- Nov 28th ^ Nov9th ---- Nov 16th
In this case for being recoverable between Nov 9th till Nov 16th (which is recovery window) , RMAN requires Nov 1st backup for recovery at any time between Nov 9th and Nov 14th. In addition, RMAN uses Nov 14th backup for recovery after that.
This shows better picture. Having recovery window of 7 days does not result to make Nov 1st backup as obsolete.