Archivelog Mode vs Noarchivelog Mode

NOARCHIVELOG mode:

1.  The Redo Log Files are overwritten each time a log switch occurs, but the files are never archived.

2.  When a Redo Log File (group) becomes inactive it is available for reuse by LGWR.

3.  This mode protects a database from instance failure, but NOT from media failure.

4.  In the event of media failure, database recovery can only be accomplished to the last full backup of the database     

5.  You cannot perform tablespace backups in NOARCHIVELOG mode.

6.  When the last redo log is written, the database begins overwriting the first redo log again

7.  Here we can only go for cold backup.Generally in this mode complete recovery is not possible 

e.g., Full Database Backup - NOARCHIVELOG Mode

SQL> BACKUP DATABASE;

ARCHIVELOG mode –

1.  Full On-line Redo Log Files are written by the ARCn process to specified archive locations, either disk or tape – you can create more than one archiver process to improve performance. 

2. A database control file tracks which Redo Log File groups are available for reuse (those that have been archived).

3.  The DBA can use the last full backup and the Archived Log Files to recover the database.

4.  A Redo Log File that has not been archived cannot be reused until the file is archived – if the database stops awaiting archiving to complete, add an additional Redo Log Group.

5.  When you are working with RMAN, ensure that the database runs in ARCHIVELOG mode.

6.  It requires additional disk space to store archived log files.

7.  It is important that the directory containing the archived log files doesn’t become full because if it does, the ARCH thread wouldn’t be able to archive the redo log files. The DBA has to continuously monitor the used-space percentage in the archive directory.

8.  In archivelog mode cold and hot backups are possible. We can recover our database upto the last point of failure.

e.g., Full Database Backup - ARCHIVELOG Mode

SQL> BACKUP DATABASE PLUS ARCHIVELOG;