by Ken Task.
At ALL in this thread ...
Check what's in your mdl_task_adhoc table for references to the backup's pending.
You can truncate the table without any ill affect.
To reclaim space, look in moodledata/temp/backup/ for any hashnamed directories (lots of letters/numbers) as those were used to build backups. With the exception of a running automated backups, those directories and be manually removed to re-claim space.
IF running autobackups, point those to a designated directory outside of moodledata/filedir/. You'll be able to see which ones are successful and remove some if one needs more space more easily.
'SoS', Ken