Keep running out of space, where have my harddrive space gone?

I have an idea about what might be the problem here - it could be a "classic" issue with mounted volumes.

My theory is that at some point, one of your mounted NAS disks in /media/fantasio/xxx actually didn't mount (maybe your NAS wasn't turned on, took too long to start etc.), and you wrote some data to the folder (it would seem appr. 70 GB of data).

This time however, instead of writing to the NAS disk, you actually wrote to the system disk, in the folder where you would usually mount the NAS (/media/fantasio/xxx).

Now the next time the NAS drives are mounted, the data already written "disappears", and is not visible on the filesystem at all - but it's still there.

To check if this is the case (which I strongly suspect), you should unmount all your NAS disks. Now check each folder where you mount your NAS for existing data, i.e.:

• /media/fantasio/data
• /media/fantasio/backup
• /media/fantasio/downloads
• /media/fantasio/media

I'm certain that when unmounted, one of these folder has some hidden content - remove it!

This is sort of a duplicate of this Q&A on superuser.com.