DB2 - What is the difference between online backup and AUTO_DB_BACKUP?
AUTO_DB_BACKUP means DB2 will take a backup based on when it feels it should do so. The things that influence the taking of a backup are:


Never completed a full backup
Time elapsed since the last full backup was a specified number of hours
Transaction log space consumed (with archival logging enabled), since the last full backup is a specified size.


In order to have AUTO_DB_BACKUP working, you also need to have AUTO_MAINT turned ON as well. I would also wager a guess that in order to enable the scheduling part, you may need to have the DBM CFG HEALTH_MON turned to ON as well.

Most DB2 DBAs I talk to turn off HEALTH_MON and AUTO_MAINT because of the performance issues encountered. DB2 may choose to exercise maintenance and backups when it is least convenient for you. So I would recommend against using them, unless you are using BLU under DB2 10.5. Then it sounds like AUTO_MAINT may be more important again.

Anyway, an online backup is just a backup while users are still engaging the database and/or the database is activated. You can take online or offline backups regardless of whether or not you have AUTO_MAINT and AUTO_DB_BACKUP enabled. You probably want online backups enabled if you wish to use AUTO_DB_BACKUP in case DB2 decides to take a backup in the middle of the day. Otherwise it could either fail to backup, or kick users off the system. I'm not sure which as I've never tried. Like I said, I steer clear of HEALTH_MON and AUTO_MAINT.

This way I can either take scripted backups when I want them scheduled via a job scheduler. Or I can take an on-demand online or offline depending on the situation.