Operating System Backup Options

There are only two physical database backup options:

1. physical backup with archiving and
2. physical backup without archiving.

Each of these options corresponds to the mode of operation of the database. In ARCHIVELOG mode all online redo logs are archived before being overwritten. In NOARCHIVELOG mode, online redo logs^[1] are overwritten without being saved. Both modes can be set by the DBA using the ALTER DATABASE command. The Oracle database can be backed up after it is shut down, called a cold backup, or while it is running, called a hot backup. A cold backup can be applied to a database operating in either ARCHIVELOG or NOARCHIVELOG mode. If it is backed up hot, the database must be operating in ARCHIVELOG mode. In this mode, all database changes are saved in a series of log files called archive logs. If the DBA makes a database backup in ARCHIVELOG mode, the DBA is making a database backup with archiving. When a DBA performs a database backup with NOARCHIVELOG mode turned off, the DBA is performing a database backup without archiving. In this course, we describe a database using archiving as an ARCHIVELOG database. The database running without archiving is called a NOARCHIVELOG database.

Operating system backup with archiving allows you to recover the database to the point of failure after a media failure. It also allows point-in-time recovery, also called incomplete recovery. In this case, you can choose to recover the database from any time between the last backup and the media failure.

When you use this option, the database must be operating in ARCHIVELOG mode. With an ARCHIVELOG database, you can choose different methods, like closed or open database backup to back up your database. You will learn these methods in detail in the following lessons.

If a database is running in NOARCHIVELOG mode, you must use the closed database backup method. This method requires the DBA to shut down the database when a backup is performed. This is covered in the next lesson.

It is important to remember that operating physical backups without archiving only allows the NOARCHIVELOG database to recover to the point of the last backup after a media failure. The following table indicates the options available for database backups and methods that can be used for each option:

METHODS	OPTIONS
	ARCHIVELOG mode	NOARCHIVELOG mode
Closed database (cold ) backup	Yes	Yes
Open database (hot) backup	Yes	No

The next lesson lists the steps required to prepare for closed database backups.

[1]online redo logs: Oracle online redo logs are essentially transaction journals that continuously track all changes made to the database. These logs are critical for recovering the database to a consistent state in case of an unexpected system failure.