Everything says my disk is full

Attached is the picture I see in Webmin showing my used space under /. This problem started about a month ago. Thinking that I perhaps had some hidden file or a file that was remaining due to being attached to a process I just upgraded to a 256GB SSD, which is now showing full as well. I have looked at the following issues and none of them had applied to me. I can't even locate the file(s) that is the culprit. I wish it was a log file but all of my log files show WAY less than 200GB+. Is there a way to scan the drive, bit by bit, to find where all of this space is going?

Screen shot of WebMin

• Ubuntu says the disk is full but it's not
• Ubuntu One says that my account is full, but it's not
• Ubuntu thinks Btrfs disk is full but it's not
• Why can't Ubuntu see any free space?
• My root partition keeps filling to 100% capacity, but I can't figure out why!

I can't get df -h to format corecttly so I've attached a screen shot.

Output of df -h

Filesystem                         Size  Used Avail Use% Mounted on
tmpfs                              3.2G  3.8M  3.2G   1% /run
/dev/mapper/ubuntu--vg-ubuntu--lv  228G  227G     0 100% /
tmpfs                               16G     0   16G   0% /dev/shm
tmpfs                              5.0M     0  5.0M   0% /run/lock
tmpfs                              4.0M     0  4.0M   0% /sys/fs/cgroup
/dev/sda2                          976M  220M  690M  25% /boot
/dev/sdg1                           29G  112K   29G   1% /media/USB_Key
/dev/sda1                          511M  7.9M  504M   2% /boot/efi
/dev/sdf1                          7.3T  3.9T  3.5T  54% /media/USB_Backup
/dev/mapper/NAS                     11T  6.7T  4.4T  61% /media/NAS
tmpfs                              3.2G  4.0K  3.2G   1% /run/user/1000

Screen Shot of ncdu output

Screen shot of ncdu output of /media directory

Also, when I run ncdu on / and exclude the /media directory (which has my external mounts) this is what ncdu reports at the bottom:

Total disk usage: 36.8 GiB Apparent size: 128.0 TiB Items: 839806

Solution 1:

What it ended up being is that despite it looking like /media/USB_Backup was monted, it actually wasn't and my backups where going to my primary drive. I deleted the entry for that drive in etc/fstab, rebooted, cleared the directory, recreated the line in fstab again, rebooted again, and now it is actually pointing to the external drive. I tested by rebooting with it unplugged and it was empty, rebooted with it plugged in and it had contents. My primary drive is now showing almost empty. Thanks to @OrganicMarble for making me unmount the drives (I was being lazy). Probably would have never found it, if not for that. Thanks everyone.