Ok... Have updated to moodle 2.2.7 it meeded doing anyway.
The attached drive in this case was a USB. We basically did course backups, so when the odd user, trashed their course - we could get it back quickly - it happens.
Basically the backup up usb drive got full so instead of stopping the files started to save in the DATA_FOLDER.
Looking at the backup logs everything looked fine. It wasn't until ouyr server started complaining that its 1TB hard drive was full I knew something was up.
I have run a new backup and told it to keep just 1 file - hopeing that these would delete all the old ones. It just deletes one file, before adding the new one, so the 20 or so old backups remain.
This is in well over 150 courses.
And each file has to be deleted individually.
This is not good
thanks for replying btw