Ideally, you should back up the database indexes once every day that the system is being actively monitored by the NetBackup administrator. If you choose to back up after every job, you will end up thrashing your drives. Also, because only two alternating copies of the indexes are kept on tape by default, you will end up corrupting your index tape backups quickly if your online disk index does get corrupted. Backing up less often than once a day will result in the need to rebuild indexes off of tape for the most recent backups should a restore be needed and the online index should become corrupted.