We used to run course backups as a separate cli cron and changed the process priority using "nice".
Since upgrading to 3.9 automated_backups.php now push a list into adhoc tasks.

This has removed the ability to control the process priority of the backups and is causing severe performance issues with I/O as they are processed as a foreground task during "interactive" periods.

Is there a way to limit the I/O priority of the course backup adhoc tasks ?