Tuesday, December 6, 2011

RMAN Incrementally updated backups

This feature enables you to create an image of data file and roll forward the image copy backups with regularly create incremental backups of the database. The image copy is updated with all changes up to the SCN of incremental backup that was taken.

This feature reduces the restoration time especially when Recovery time Objective (RTO) is set for mission critical databases. In case of any recovery required you never have more than one day of redo logs to apply.

For example: - Run this script on a regular basis to implement an updated backup strategy
RUN {
ALLOCATE CHANNEL C1 DEVICE TYPE DISK FORMAT ‘/oradata/rman/backup.%u’;
RECOVER COPY OF DATABASE WITH TAG 'incr_backup_update';
BACKUP INCREMENTAL LEVEL 1 FOR RECOVER OF COPY WITH TAG 'incr_backup_update' ATABASE;
}

• The BACKUP INCREMENTAL LEVEL 1... FOR RECOVER OF COPY WITH TAG... command creates a level 0 backup of the datafile, if there is no level 0 backup. In all subsequent runts, It produce’s level1 incremental backups of data file.

• The RECOVER COPY OF DATABASE WITH TAG... command causes RMAN to apply any incremental level 1 backups to a set of datafile copies with the same tag and roll forwards the image copies.

Incremental Merge backup’s strategy is the fast and easy way to restore entire database.

If you are backing up your database using Incremental merge backup then you can recovery the entire database very fast and easily by using SWITCH command. This command will point the controlfile to the backup of the data files that are present on the disk.

Let’s simulate a database failure by removing all or few data files. Make sure your database has been successfully backed up before you remove the files.

Mount the database and use SWITCH DATABASE TO COPY command to point the database to the backups available on disk.

SYS@DBTEST>startup mount
SYS@DBTEST>switch database to copy;
SYS@DBTEST>Recovery the database;
SYS@DBTEST>Alter database open;

Please note that we didn’t restored backup from backup disk or media, we have pointed the database to backup.

Regards
Satishbabu Gunukula
http://www.oracleracexpert.com

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