A database in computing is a structured collection of data that is electronically accessible and stored. A database improves data access to users via query languages, enhances data security and integrity, while reducing its redundancy, so it is widely implemented for business storage.
Among all sorts of databases on the market, Oracle database has long been popular with global users. Oracle backup and recovery earn deservedly increased attention as many businesses store their mission-critical data on the database.
Thus, Oracle launches its built-in tool for backup and recovery, RMAN (Recovery Manager), in Oracle release 8.0. Still, some may be puzzled by the utility about its components, features, and how it works. Go through the blog for answers.
What is Oracle RMAN?
Recovery Manager (RMAN) is an Oracle database program that automates the management of your backup policies and conducts backup and recovery operations on your databases. Database file backup, backup, and recovery are all made much easier.
Oracle Recovery Manager supports a lot of practical functions such as block media recovery, automatic database duplication, backup encryption, and cross-platform data transformation, and carries out all maintenance work throughout the process.
Oracle RMAN Components
RMAN client:The client program is in charge of controlling backup and recovery procedures for a target database. The RMAN client can connect to a target database using Oracle Net, therefore it can be installed on any system that has an Oracle Net connection to the target host.
Target database: A database where the control files, data files, and optionally archived redo logs are stored for RMAN backup and recovery. The control file keeps target database metadata and RMAN operations information. Server sessions that are connected to the database execute backup and recovery.
Recovery catalog database: A database includes a recovery catalog that can be used for multiple target databases, optionally for RMAN but necessarily for physical standby database use, and metadata of RMAN backup and recovery operations.
Recovery catalog schema: Recovery catalog database user who has RMAN metadata tables. RMAN periodically updates the metadata of the target database control file to the recovery catalog.
Physical standby database: A duplicate of the primary database that receives updates from redo of the primary database for failover should the former becomes unavailable.
Fast recovery area: A disk location to store recovery-related files like RMAN backups and control file, which is automatically managed by RMAN and Oracle DB.
Media management software: A vendor-specific program that makes RMAN backup to a storage system like tape possible.
Media management catalog: A vendor-specific depository for media management application metadata.
Oracle Enterprise Manager: A browser-based interface that enables functions like RMAN backup and recovery.
RMAN Features
Backup sets: Composed of backup pieces, or binary files unique to RMAN, which allows DBAs to protect control files, archive logs, and other information.
Archived redo logs: Every Oracle database has a redo log that records database changes. Archived redo logs preserve offsite redo logs group and can be used to recover inconsistent database from improper database shutdown.
Flash recovery: Flash recovery is a directory that stores RMAN backups, which includes image copies, control files, online and archived redo logs, and flashback logs. It removes obsolete backups for new data based on the DBA policies.
Media recovery: Datafile media recovery restores a damaged file, while block media recovery can restore data blocks within the datafile.
Backup encryption: RMAN backup sets encryption denies unauthorized users with 3 modes: transparent (default, use Oracle software keystore), password (passwords for both backup and restore operations), and dual mode (either keystore or a password).
How RMAN Works for Oracle Backup and Recovery?
RMAN Backup Overview:
1. Launch RMAN and connect to a target database and a recovery catalog (if applicable):
Start the RMAN client on the OS command line.
% rman
RMAN>
Enter the “CONNECT” command.
RMAN> connect target /
2. Configure RMAN default settings if needed.
Run the “SHOW ALL” command to view.
Change the values you want. Use “CONFIGURE DEFAULT DEVICE TYPE” to specify locations, or “ALLOCATE CHANNEL” to change the tunnels, and more.
Use the “CONFIGURE ... CLEAR” command to return to default settings.
CONFIGURE FEATURENAME CLEAR;
3. Execute command lines to backup.
RMAN> BACKUP DATABASE;
For more details and RMAN backup scripts, refer to How to Take Oracle Backup Step by Step?
RMAN Recovery Overview:
1. Start RMAN and connect to the database and recovery catalog.
2. Mount the database but do not open it.
STARTUP MOUNT;
3. Run “SHOW ALL” to “CONFIGURE” necessary channels or devices.
4. Provide passwords for encrypted backup sets.
SET DECRYPTION IDENTIFIED BY passwordforbackup;
5. Restore or recover an Oracle database with one of the RMAN commands.
RMAN> RESTORE DATABASE;
RMAN> RECOVER DATABASE;
6. Open the database with the RESETLOGS
RMAN> ALTER DATABASE OPEN RESETLOGS;
This is a basic process of recovering the whole database, and different recovery targets may require different steps. If you want to see more details, visit Restoring an Oracle Database from RMAN Backups.
RMAN Advantages
Skip unused data blocks to improve backup efficiency and speed.
Backups compression reduces backup storage needed for new data blocks.
Backup encryption enhances data security.
Block recovery avoids database downtime during recovery.
Choose the most appropriate backups for recovery.
Convert the tablespace to another OS with cross-platform data conversion.
Limitations
You are restricted by the following limitations when you use RMAN through OEM’s CLI or GUI.
1. RMAN stores backup information in the recovery catalog, which is held in a separate database, thus producing more overhead and management work.
2. The high CPU consumption during database backup may force the users to choose between database and backup performance.
3. Restore or recovery is challenging in a disaster scenario where you lose the recovery catalog and production database, the former automatically restores the database from backups.
How to Backup and Recovery Oracle Database without Command?
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