Oracle RMAN : Incrementally Updated Backups

We have learned about incremental backups and how to make these incremental backups faster. Now we will discuss incrementally updated backups

• Assume we have very huge size database say around 50-60TB, there are few challenges we may face while performing backup like making backup faster and keeping recovery time as less as possible.
• Generally recovery is done after restore and restore takes all the time, so we need to concentrate on reducing this restore time.
• For backup minimization time we have enough option of incremental backups but in order to reduce restore time, we go new Incrementally updated backups
• Using incrementally updated backup method, RMAN rolls forward the backup taken of an image copy with subsequent incremental backups. With incremental backups updated with all the changes since last incremental level backup
• Using RMAN, database can be just switched over this updated image copy, rather than restoring them back to original files location
• Since we are not restoring files, restore will be very very minimum and to recover the same, redo logs will be less and it would be only last incremental backup
• Thus within few minutes, we will be able to restore and recover the database
• One of the major condition while using this method is use of large enough FRA (Fast Recovery Area) in order to take full image copy database backup. RMAN will look for updated image at FRA only

Now we will discuss how exactly this works

We can use RUN block to execute set of RMAN commands

RUN

{

RECOVER copy of database

with tag 'tech_db_incr';

BACKUP

incremental level 1

for recover of copy with tag 'tech_db_incr' database;

}

Assuming you running this RUN block daily, here is what happens every day

Day 1 : On first day RECOVER command does nothing , to apply incremental backups a level backup is needed, since there isn't one existing yet BACKUP command will create level 0 image copy of database backup

Day 2 : On second day, as level 0 backup exists the BACKUP command will create level 1 incremental backup. There wont be any work for RECOVER command on second day as well

Day 3 Onward : from third day onward RECOVER command will update the image copy with previous days level 1 incremental backup daily 

To do point in time recovery of this image copy, the available time window is only until level 0 backup, so if we created level 0 backup of database on Aug 6, we can not recover it using incrementally updated backups till Aug 4 or so.