How to find which backup files can be deleted or not need anymore?

$ rman

Recovery Manager: Release 11.2.0.1.0 - Production on Fri Dec 27 22:07:16 2013

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RMAN> connect target /;

connected to target database: PROD (DBID=246965557)
RMAN> report obsolete;

RMAN retention policy will be applied to the command
RMAN retention policy is set to redundancy 2
Report of obsolete backups and copies
Type                 Key    Completion Time    Filename/Handle
-------------------- ------ ------------------ --------------------
Backup Set           1      27-DEC-13
  Backup Piece       1      27-DEC-13          /d01/oracle/flash_recovery_area/PROD/backupset/2013_12_27/o1_mf_ncnnf_TAG20131227T220955_9cvcbwhr_.bkp
Backup Set           2      27-DEC-13
  Backup Piece       2      27-DEC-13          /backup/rman/prod/c-246965557-20131227-00

RMAN>