Managing Backups with RMAN
| Recovery Manager (RMAN) is a client application that performs backup and recovery operations on databases. The RMAN environment may consist of components like a target database, RMAN client, recovery catalog, recovery catalog schema, standby database, media management application, media management catalog, and the OEM. Of these components, the target database and RMAN client are necessary for RMAN operation. The RMAN client application uses database server sessions to perform all backup and recovery tasks. When you connect the RMAN client to a target database, RMAN gets server sessions on the target instance to perform the necessary operations. The RMAN client uses internal PL/SQL packages to communicate with the target database and recovery catalog.
When you run RMAN in command-line mode, the output will be sent to the terminal if the LOG option is not specified. The output from currently executing RMAN jobs is also written to the V$RMAN_OUTPUT view. The RMAN repository has the metadata on target databases. RMAN always stores this information in records in the control file. You can create a recovery catalog in an external Oracle database to store this information. The advantage of an external recovery catalog is longer history retention for metadata compared to the smaller size of control file. For Oracle Database 10g Release 2, the FLASHBACK DATABASE command has been improved to quickly return a database to a prior time without restoring data files and performing media recovery. Also the reporting on RMAN through OEM has been improved.
Oracle recommends the use of a flash recovery area and that you run your production databases in ARCHIVELOG mode for RMAN backups. Always use the flash recovery area as an archive log destination on a separate disk to prevent a single point of failure for the entire database. The size of the flash recovery area depends on the size and activity levels of the database and recovery objectives. The DBID and the DB_UNIQUE_NAME should be noted to help with scenarios like recovery of a lost database control file. RMAN creates database backups, which could be stored as image copies or backup sets. Image copies are exact byte-for-byte copies of the files, while backup sets are logical entities consisting of several physical files called backup pieces. When you create image copy backups through RMAN or OEM, RMAN will create a record of those image copies in the RMAN repository. RMAN uses these copies during database restore and recovery. RMAN will only use those files in the RMAN repository for restore operations. Backup pieces use an Oracle proprietary format to store the file contents. They can be accessed only as part of backup sets and not individually. When you back up data files into backup sets, free data blocks (with no data) are not written into the backup pieces in order to save space. This process is known as unused block compression. These backup sets can be compressed using an additional binary data compression algorithm during the writing stage to save some more space. The additional compression will affect the CPU and database performance and should be used if disk space is preferred over backup speed. RMAN uses server sessions to perform backup and restore tasks. It supports parallelism, and you can have multiple channels and sessions to speed up the backup process.
More details on RMAN, channels, and parallelism are available in Oracle Database Backup and Recovery Basics 10g and Oracle Database Backup and Recovery Advanced User's Guide. You can set up the device properties, parallelism, backup type, and location from OEM under Database Home page > Maintenance property > Backup/Recovery. Important Points on RMAN During Database UpgradeRefer to the RMAN compatibility matrix before you do a database upgrade. Each component in the RMAN environment has a release number associated with it. The following components are usually present: RMAN executable, recovery catalog database, recovery catalog schema in the recovery catalog database, target database, and auxiliary database (duplicate or standby database). When you upgrade a database, make sure that the RMAN catalog schema version is greater than or equal to the catalog database version. The catalog schema version is the version of dbms_rcvcat, dbms_rcvman packages, and catalog tables and views in the schema. The RMAN executable version should be the same as the target database version. The RMAN catalog is backward-compatible with target databases from earlier releases. RMAN will give the following errors when components are not compatible as per the matrix:
If your recovery catalog is older than that required by the RMAN client, then you must upgrade it. You will get an error if the recovery catalog version is higher than the RMAN client requirements. To upgrade the recovery catalog, do the following:
Please refer to Oracle Database Recovery Manager Reference and Oracle Database Upgrade Guide for more information on RMAN and upgrade processes. Unregister a Target DatabaseBeginning with Oracle Database 10g, you can unregister a target database from the recovery catalog by using a new RMAN command (unregister) in one of the following ways (where <database_name> is the name of the target database to be unregistered and noprompt implies that RMAN should not prompt for confirmation before unregistering): rman> unregister database <database_name>; rman> unregister database <database_name> noprompt; If RMAN is connected to the target database where it is registered, you need not specify this name. If the database name is unique, provide the database_name argument to identify the database to unregister. If RMAN is not connected to the target database and the database_name is not unique in the recovery catalog, use SET DBID to identify the database. Glimpse of Oracle Database 10g Release 2This section includes a quick summary of the feature improvements in Oracle Database 10g Release 2.
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EAN: 2147483647
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