Recovering After the Loss of Archived Redo Log Files: Scenario

If the database is operating in ARCHIVELOG mode, and if the only copy of an archived redo log file is damaged, then the damaged file does not affect the present operation of the database. The following situations can arise, however, depending on when the redo log was written and when you backed up the datafile.

If you backed up . . .	Then . . .
All datafiles after the filled online redo log group (which is now archived) was written	The archived version of the filled online redo log group is not required for complete media recovery operation.
A specific datafile before the filled online redo log group was written	If the corresponding datafile is damaged by a permanent media failure, use the most recent backup of the damaged datafile and perform incomplete recovery of the tablespace containing the damaged datafile, up to the damaged log.

Caution:

If you know that an archived redo log group has been damaged, immediately back up all datafiles so that you will have a whole database backup that does not require the damaged archived redo log.