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RMAN Incremental Backups

February 1, 2014

RMAN Backup Strategy can be :
=========================================================

Sunday     Level (Full Bakup) 0 (Every half hour archive backups)
 ...................Monday    Diff level 1 (Every half hour archive backups)
 ......................................Tuesday    Diff Level 1 (Every half hour archive backups)
 Wednesday Cumulative Level 1 (Every half hour archive backups)
 .........................................................Thursday  Diff Level 1 (Every half hour archive backups)
 .............................................................................Friday        Diff level 1 (Every half hour archive backups)
 Saturday   Cumulative level 1 (Every half hour archive backups)
Sunday Level 0 (Every half hour archive backups)

RMAN can create multilevel incremental backups.

Each incremental level is denoted by a value of 0 or 1.

A level 0 incremental backup, which is the base for subsequent incremental backups, copies all blocks containing data.

The only difference between a level 0 incremental backup and a full backup is that a full backup is never included in an incremental strategy.

A level 1 incremental backup can be either of the following two types:
========================================================================
(1) A differential backup, which backs up all blocks changed after the most recent incremental backup at level 1 or 0
The following command performs a level 1 differential incremental backup of the database:

RMAN> BACKUP INCREMENTAL LEVEL 1 DATABASE;
———————————————————————————————————————————–
(2) A cumulative backup, which backs up all blocks changed after the most recent incremental backup at level 0
The following command performs a cumulative level 1 incremental backup of the database:

RMAN> BACKUP INCREMENTAL LEVEL 1 CUMULATIVE DATABASE; # blocks changed since level 0

Incremental backups are differential by default.

Note:
Cumulative backups are preferable to differential backups when recovery time is more important than disk space, because fewer incremental backups need to be applied during recovery.

When deciding how often to take full or level 0 backups, a good rule of thumb is to take a new level 0 whenever 50% or more of the data has changed. If the rate of change to your database is predictable, then you can observe the size of your incremental backups to determine when a new level 0 is appropriate.

The following query displays the number of blocks written to a backup set for each datafile with at least 50% of its blocks backed up:

SELECT FILE#, INCREMENTAL_LEVEL, COMPLETION_TIME, BLOCKS, DATAFILE_BLOCKS
FROM V$BACKUP_DATAFILE
WHERE INCREMENTAL_LEVEL > 0
AND BLOCKS / DATAFILE_BLOCKS > .5
ORDER BY COMPLETION_TIME;

Reference:

http://docs.oracle.com/cd/B19306_01/backup.102/b14192/bkup004.htm

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