NOARCHIVELOG MODE protects database from instance failure but not from media failure - Oracle Redo Log

Discussion

• Nirja Shah   -Posted on 24 Sep 15
  - A database can operate in two distinct modes: NOARCHIVELOG mode (media recovery disabled) or ARCHIVELOG mode (media recovery enabled).
  
  - NOARCHIVELOG Mode (Media Recovery Disabled)
  - If a database is used in NOARCHIVELOG mode, then the archiving of the online redo log is disabled.
  - Information in the database's control file indicates that filled groups are not required to be archived.
  - Therefore, as soon as a filled group becomes inactive, the group is available for reuse by the LGWR process.
  - NOARCHIVELOG mode protects a database only from instance failure, not from disk failure.
  - Only the most recent changes made to the database, stored in the groups of the online redo log, are available for crash recovery or instance recovery.
  - This is sufficient to satisfy the needs of crash recovery and instance recovery, because Oracle will not overwrite an online redo log that might be needed until its changes have been safely recorded in the datafiles.
  - However, it will not be possible to do media recovery.
  
  - ARCHIVELOG Mode (Media Recovery Enabled)
  - If an Oracle database is operated in ARCHIVELOG mode, the archiving of the online redo log is enabled.
  - Information in a database control file indicates that a group of filled online redo log files cannot be reused by LGWR until the group has been archived.
  - ARCHIVELOG mode permits complete recovery from disk failure as well as instance failure, because all changes made to the database are permanently saved in an archived redo log.

➨ Post your comment / Share knowledge