If a backup fails, the backup program attempts to recover.
If backup fails during either the checkpoint at the start of backup or the checkpoint when backup is complete, it performs normal checkpoint recovery.
If backup fails between checkpoints, it rolls back the backup.
If the system fails at any time between the initial and final checkpoint and you must restore the database, you must do so using an older set of backup tapes or disk files.
If the system fails during the final checkpoint after a FULL backup, you can restore from the backup tapes or files you have just created.