What is the difference between obsolete and expired status?

A status of "expired" means that the backup piece or backup set is not found in the backup destination. With tape management systems, the automated tape library routines will expire files on the tape once a certain period of time has passed. RMAN uses this terminology to say that the tape management system has expired the file. It is no longer available. Therefore, the backup piece is expired as well.

A status of "obsolete" means the backup piece is still available, but it is no longer needed. The backup piece is no longer needed since RMAN has been configured to no longer need this piece after so many days have elapsed, or so many backups have been performed. RMAN's retention configuration determines when a backup piece becomes obsolete.