If OpenX database is large, upgrading could make it even larger because of creating data backup.

Starting from OpenX v2.4 the upgrade wizard will create a backup for each table affected by the changes. In order to prevent OpenX upgrade wizard from creating backups create empty file NOBACKUPS in "/var" directory, the full path should be "/var/NOBACKUPS".

Consider that although the backups are created during upgrading process this step is not replacement for creating a full system backup before the upgrade process begins.