Oracle RMAN

Recovery Manager (RMAN) is client/server utility provided by oracle to perform backup and recovery operations on oracle database. RMAN is available in command-line interface as well as in Enterprise manager GUI. RMAN is part of oracle database and does not require separate installation or configuration. RMAN was firstly introduced with oracle 8.0. With RMAN, process of backup and recovery is easy, reliable and fast.

Oracle supports two methods to perform backup and recovery. First method is known as user-managed backups, in this method backup of database files is taken using operating system commands and SQL *Plus commands are used to perform recovery. In second method, RMAN is used to perform all backup and recovery operations. RMAN has certain advantages over user-managed backups. Following are main advantages of RMAN over user-managed backups


1- If you want to take an online backup using user-managed technique, all online read/write tablespaces must be put in backup mode. If you failed to do so, database recovery may not be possible when required. With RMAN, no tablespace is required to be put in backup mode.

2- RMAN allows incremental backups. In incremental backup, only thatdata blocks are copied which have changed after previous backup. In user-managed backups all data blocks are copied every time.

3- RMAN checks for data block corruption and archive log corruption during backup.

4- RMAN omits data blocks that have never been used. Operating systemcommands used in user-managed backup copy all the database files with all blocks. So the size of RMAN backup is usually small.


In addition to above, RMAN maintains metadata of its operations. This metadata is called RMAN repository. RMAN repository can be kept in target database (database which is being backed up) control file or in a separate database schema called recovery catalog. This repository stores information about location of backup sets, target database schema and current RMAN settings. Metadata can be accessed by using LIST, SHOW and REPORT commands. If you are using recovery catalog, certain views are available to query RMAN repository.


When database is recovered using RMAN, RMAN requires metadata to find location and type of backups. Without this repository, RMAN can not perform restoration and recovery operation.

Visit following link to find an example of RMAN backup script,


http://exploreoracle.com/2009/09/06/rman-script-to-take-full-database-backup/


Visit following link to find an example of database recovery using RMAN.


http://exploreoracle.com/2009/09/12/rman-recovery-restore-controlfile/

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