I tried out the backup module (core 2.0.5), which reported that no backups were carried out. After a couple of days the backup disk was full - the backups were being created but were not reported in the dashboard.
Although I set it to only keep one backup copy, earlier copies were not being removed hence the disk filling.
Monitoring showed the disk being filled on the schedule I set (n.b. colours on the file system usage graph are wrong).
I deleted the backup files manually and removed the backup module. Appears to use "duplicity" by the way, which is not removed when the module is removed.