RMAN INCREMENTAL BACKUP Differential vs Cumulative

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RMAN INCREMENTAL BACKUP

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Oracle Database RMAN INCREMENTAL BACKUP STRATEGY Differential vs Cumulative
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RMAN INCREMENTAL BACKUP STRATEGY
Differential VS Cumulative

Backup Options:
- User managed backups
- RMAN backups - Many different options
- Logical backups - Data Pump

RMAN Incremental Backups
An incremental backup copies only data blocks that have changed since a previous backup.
Incremental backups are multilevel backups.
- Level 0 forms the foundation for subsequent incremental backups and copies all blocks containing data
- Level 1
- differential incremental Level 1 backup backs up all blocks changed after the most recent incremental backup at level 1 or 0
- cumulative incremental Level 1 backup backs up all blocks changed after the most recent incremental backup at level 0

Knowledge fact:
Incremental backups are differential by default.
Incremental backups at level 0 can be either backup sets or image copies, but incremental backups at level 1 can only be backup sets.
If no level 0 backup is available in either the current or parent incarnation, RMAN copies all blocks that have been changed since the file was created. Otherwise, RMAN generates a level 0 backup.

About Block Change Tracking:
The block change tracking feature for incremental backups improves incremental backup performance by recording changed blocks in a block change tracking file.
The block change tracking file is a small binary file within the database which RMAN uses to track changed blocks as redo is generated.
If block change tracking is enabled, then RMAN uses the change tracking file to identify changed blocks for incremental backups, thus avoiding the need to scan every
block in the data file.
RMAN only uses block change tracking when the incremental level is greater than 0, because a level 0 incremental backup includes all blocks.
In an Oracle Real Application Clusters (Oracle RAC) environment, the change tracking file must be located on shared storage accessible from all nodes in the cluster.

Enabling Block Change Tracking:
- Start SQL*Plus and connect to a target database with administrator privileges.
- Ensure that the DB_CREATE_FILE_DEST initialization parameter is set.
- ALTER DATABASE ENABLE BLOCK CHANGE TRACKING USING FILE 'path_to_file/file_name';

PROS and CONS of each strategy:
Differential backups are faster because it only backs up blocks that have changed since the last level 0 or level 1 backup
However, recovery time takes longer take longer at recovery time.

Cumulative backups are preferable to differential backups when recovery time is more important than disk space, because fewer incremental backups must be
applied during recovery. However, it has a longer daily backup window and more disk usage.

Recovery speed: Cumulative backups are faster to restore from than differential backups because fewer incremental backups need to be applied during recovery.

Backup speed: For daily backup speed, differential backups run faster than cumulative backups because to don't duplicate the work done by previous backups.
However, differential backups take longer when doing a recovery.

Disk space usage: Cumulative backups take more disk space because they duplicate the work done by previous backups

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