On a number of Moodle instances that we look after we have automated course backup configured in conjunction with cron. Everything works as expected with the exception of the size of the automated backups.
We have inferred, perhaps wrongly!, from https://docs.moodle.org/27/en/Backup_and_restore_FAQ#Why_is_my_automated_course_backup_much_smaller_in_size_than_my_manual_course_backup.3F
that the automated backups shouldn't contain every piece of content in the course. This does not appear to be the case. The automated backups for us are the same in size as if a manual backup occurred on that day.
The result for us is that whatever 'backup | backup_auto_keep' is configured to is the factor by which moodledata storage for the particular course is consumed. For example a 50MB course with Backup -> Keep' set to 5 will result in 5 * 50MB = 250MB of storage use for the automated course backup. In our testing this has been irrespective of the changes or activity on a particular course. If the Automated backup configuration determines that a backup is needed then all course content is duplicated in moodledata rather than the delta.
What I would like to know is whether this behaviour is normal, i.e. if you want 5 copies you get 5 full copies, or whether any of the automated course backup settings impact the size? Does, for example, 'Include activities and resources' mean a) include a reference and the asset or b) include just a reference.
It has occurred to me that were the automated backup only to include references to content assets in the automated backup file then, upon downloading such a backup the system would have to go and create an archive with the actual assets so I am not surprised by what I'm seeing I just can't reconcile it with the FAQ in the documentation.