Online redo logs vs backup

Question

Below quoted sentence is from Oracle documentation
"Online redo logs, unlike archived logs, should never be backed up. The chief danger
associated by having backups of online redo logs is that you may accidentally restore
those backups without meaning to, and corrupt your database"
Can any one explain , how the database will be corrupted if we backup online redo logs. I am having a hard time to understand this quote
thanks for your help
shajan

Answer 1

Redo log file contents is very dynamic. It changes minute after minute, so a backup is useless if you try to do it online. (In fact there is no command to perform such backup).
Let's suppose you shutdown (normal, immediate or transactional) The contents of the redo log files become useless as the checkpoint process has already taken place, so it is enough to have a copy of all of the consistent datafiles to have the last applied transaccion.
In a recovery scenario with archivelog it is important to keep all of the requiered archivelog files plus all of the online redo log files.
In case of a missing logfile it is useless to have a backup of it. If you ever had one, and you tried to restore it, an error would arise, warning you that the contents of the logfile is inconsistent with the expected scn. The only way you can succeed is to have them multiplexed and have them on different paths, just to reduce to probability of loosing all of the members of a group.
rman does not perform backup of redo log files. Classical theory of backup/recovery states that during a hot backup it must be backed up the archive log files, not the redo log files.