A backup is a copy of data. This copy can include important parts of
the database such as datafiles, which contain user data, and the server
parameter file and control file, which contain configuration
information.
The main purpose of a backup is as a safeguard against unexpected data loss and application errors. For example, a disk may fail, causing the loss of datafiles. You can restore a backup of the data and reconstruct the lost data through media recovery. Media recovery refers to the various operations involved in restoring, rolling forward, and rolling back a backup of database files.
You have two ways to perform backup and recovery of an Oracle database: Recovery Manager (RMAN) and user-managed techniques. RMAN is an Oracle Database utility that can back up, restore, and recover database files. It is a feature of Oracle Database and does not require separate installation. You can also use operating system commands for backups and SQL*Plus for media recovery. This technique, also called user-managed backup and recovery, is fully supported by Oracle, although use of RMAN is recommended because it is more robust and simplifies administration.
Oracle Flashback Technology is an alternative to traditional backup and recovery. You can use flashback features to view past states of data, and move data back and forth in time, without restoring data from backups. Instead, you can issue a single command to rewind your entire database, or a single table, to a time in the past. The flashback features of Oracle Database are more efficient and less disruptive than media recovery in most circumstances in which they are applicable.
No matter which backup and recovery tool you use, it is recommended that you configure a flash recovery area to manage your recovery-related files.
Oracle Database can write archived logs to the flash recovery area. RMAN can store backups in the flash recovery are and restore them from the flash recovery area during media recovery. The flash recovery area also acts as a disk cache for tape.
Oracle Database recovery components interact with the flash recovery area to ensure that the database is completely recoverable by using files stored in the recovery area. All files necessary to recover the database following a media failure are part of the flash recovery area.
The following recovery-related files are stored in the flash recovery area:
Oracle Database and RMAN create files in the flash recovery area until the space used reaches the recovery area disk limit. When it must make room for new files, Oracle Database deletes files from the flash recovery area that are obsolete, redundant, or backed up to tertiary storage. Oracle Database prints a warning when available disk space is less than 15%, but it continues to fill the disk to 100% of the disk limit.
The bigger the flash recovery area, the more useful it becomes. The recommended disk limit is the sum of the database size, the size of incremental backups, and the size of all archive logs that have not been copied to tape.
The main purpose of a backup is as a safeguard against unexpected data loss and application errors. For example, a disk may fail, causing the loss of datafiles. You can restore a backup of the data and reconstruct the lost data through media recovery. Media recovery refers to the various operations involved in restoring, rolling forward, and rolling back a backup of database files.
You have two ways to perform backup and recovery of an Oracle database: Recovery Manager (RMAN) and user-managed techniques. RMAN is an Oracle Database utility that can back up, restore, and recover database files. It is a feature of Oracle Database and does not require separate installation. You can also use operating system commands for backups and SQL*Plus for media recovery. This technique, also called user-managed backup and recovery, is fully supported by Oracle, although use of RMAN is recommended because it is more robust and simplifies administration.
Oracle Flashback Technology is an alternative to traditional backup and recovery. You can use flashback features to view past states of data, and move data back and forth in time, without restoring data from backups. Instead, you can issue a single command to rewind your entire database, or a single table, to a time in the past. The flashback features of Oracle Database are more efficient and less disruptive than media recovery in most circumstances in which they are applicable.
No matter which backup and recovery tool you use, it is recommended that you configure a flash recovery area to manage your recovery-related files.
Flash Recovery Area
The flash recovery area is an optional Oracle Database-managed directory, file system, or Automatic Storage Management disk group that provides a centralized disk location for backup and recovery files. You can configure the flash recovery area when creating a database with the Database Configuration Assistant or add it later.Oracle Database can write archived logs to the flash recovery area. RMAN can store backups in the flash recovery are and restore them from the flash recovery area during media recovery. The flash recovery area also acts as a disk cache for tape.
Oracle Database recovery components interact with the flash recovery area to ensure that the database is completely recoverable by using files stored in the recovery area. All files necessary to recover the database following a media failure are part of the flash recovery area.
The following recovery-related files are stored in the flash recovery area:
-
Current control file
-
Online redo logs
-
Archived redo logs
-
Flashback logs
-
Control file autobackups
-
Datafile and control file copies
-
Backup pieces
Oracle Database and RMAN create files in the flash recovery area until the space used reaches the recovery area disk limit. When it must make room for new files, Oracle Database deletes files from the flash recovery area that are obsolete, redundant, or backed up to tertiary storage. Oracle Database prints a warning when available disk space is less than 15%, but it continues to fill the disk to 100% of the disk limit.
The bigger the flash recovery area, the more useful it becomes. The recommended disk limit is the sum of the database size, the size of incremental backups, and the size of all archive logs that have not been copied to tape.
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