This would be a little thought about Oracle database backups. It is related to my experiences that are from database that ranges from 2/3 GBytes to the greatest of over 100 GBytes, with important data but not bank data (no man death in case of data loss).
People sometimes has strange ideas about backups so i want to say my ideas.
Oracle guides on backup and recovery report a lot of options and left to final user the choice of the best option, based on his own needs.
There are full and incremental backups, tape and disk backups. I think, until databases dimensions of today (tomorrow may be other numbers) a database of 100Gb may be fully backed up on disk and then on Tape. What i want to say? What has said oracle with the introduction on Oracle 10g and flash recovery area: disks are now not so expensive time of people is expensive; tape libraries (in my opinion) are expensive. So it is important backup policy that allows a fast restore and recovery, disk backup does it. You don’t need to use expensive disks to backup a database, you don’t need to user RAID-1 for backup disks, you can use a RAID-0, maybe with SATA disks. Today a SATA disk is not so much expensive than a LTO tape. An LTO tape i think it is not more reliable than a SATA disk.
Then you can use backup your backup files on type daily on week bases to be safer.
My experience is that also an export my be a last resort type of backup. Be clear, export is not a real backup, someone still thinks that export based backup policy is good: it is terrible.
note: oracle puts on flash recovery area the archived logs. The destination of archived logs must be reliable, not RAID-0, because a failure of archiver means a stop of transactions on the database.
So, use RMAN, make full backups on disks and then save those backup on Tape. This, plus an export on user basis, my be a decent backup policy.