Incremental Backup

RMAN Incremental Backups:-

• RMAN incremental backups back up only datafile blocks that have changed since a specified previous backup. 
• You can make incremental backups of databases, individual tablespaces or datafiles.

Reason of Incremental Backups:-

• To reduce the amount of time needed for daily backups
• To save network bandwidth when backing up over a network
• To reduce backup sizes for NOARCHIVELOG databases.

Incremental Backup Algorithm:-

• Each data block in a datafile contains a system change number (SCN), 
• Incremental backup,rman reads the scn of each data block and compare to checkpoint scn of parent inc backup.

Note:-

1.   If you enable the block change tracking feature, RMAN can refer to the change tracking file to identify changed blocks in datafiles without scanning the full contents of the datafile.

Level 0 and Level 1 Incremental Backups
Incremental backups can be either level 0 or level 1.

Differential backup (for level 1 parents only):

1.  The default is differential backup, where RMAN looks for last level 1 or level 0 backup, and a differential backup only captures those data block changes that were made after those backups.  
2. Differential backups are faster because there are fewer changes stored, 
3. but they take longer at recovery time.

backup incremental level 1 database;

Cumulative backup (for level 0 or level 1 parents):  With a cumulative backup,

1. RMAN backups up all data block changes that are made after a level 0 backup. 
2. The main advantage of cumulative backup over differential is the fast recovery time,
3.  but at the expense of a longer daily backup window and more disk usage.

backup incremental level 0 database;

Advantages and disadvantages of Incremental Backup:-

Recovery speed:-

1.  Cumulative backups are faster to restore from than differential backups
2.  Because fewer incremental backups need to be applied during recovery.

Backup speed: 

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

Disk space usage:

1.  Cumulative backups take more disk space because they duplicate the work done by previous backups

  backup incremental level 1 cumulative database;
  backup incremental level 1 tablespace sdbt;
  BACKUP INCREMENTAL LEVEL 1 CUMULATIVE SKIP INACCESSIBLE DATABASE;


To view the incremental backup information:-

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;