2nd drive fills up storage space on root file system

Question

Running Ubuntu 18.04 of a 256GB SSD with full disk encryption and an additional 1TB harddisk mounted for larger files. I keep getting "Low on space" notifications because "The filesystem root /" is filling up (supposedly).

The weird thing is, when I look at Disk Analyzer, it will also count the files stored on the 1TB drive for the used space calculation of /. Most space is used by the /media/<username>/Harddisk folder, which is the mount point for the 1TB drive:

Any idea what's wrong here? Why does my 1TB drive mounted under /media/<username>/Harddisk use up space on /? I double checked with the command df -h and get the same results.

I unmounted the 1TB drive to see what happens then. The used up space disappears, but root is still almost full:

This is the SSD with full drive encryption. Its'definitely a 256GB drive:

And here's the df -h output:

$ df -h
Filesystem                       Size  Used Avail Use% Mounted on
udev                             7.8G     0  7.8G   0% /dev
tmpfs                            1.6G  2.5M  1.6G   1% /run
/dev/mapper/ubuntu--vg-root      232G  215G  5.2G  98% /
tmpfs                            7.8G  875M  7.0G  11% /dev/shm
tmpfs                            5.0M  4.0K  5.0M   1% /run/lock
tmpfs                            7.8G     0  7.8G   0% /sys/fs/cgroup
/dev/nvme0n1p2                   705M  164M  490M  26% /boot
/dev/nvme0n1p1                   511M  6.1M  505M   2% /boot/efi
//10.127.0.199/home               11T  152G   10T   2% /media/potaito/freenas_home
//10.127.0.199/users/potaito      11T   68G   10T   1% /media/potaito/freenas_potaito
//10.127.0.199/users              11T   68G   10T   1% /media/potaito/freenas_users

Answer 1

This sounds as if you have written data to one or more of the folders which are the mount-points of your HDD and network drives while nothing was mounted to a mount-point.

You can unmount the drives and then check the contents of this folders to see the contents of this folders while nothing is mounted.

Alternativly (while all drives are mounted) you can use a bind mount to see what is in this folders (mount-points) as if nothing would be mounted to them, to do that, make sure that all drives are mounted properly. Then run

sudo mount --bind / /mnt

and browse to /mnt/media/potaito/..., this folders should be empty. If one or more of this folders are not empty, you can now either delete the files or move them to your HDD or network drive.

Example:

You found files in /mnt/media/potaito/freenas_home. To remove them all use

rm -R /mnt/media/potaito/freenas_home/*

To move them all to the network drive use

mv /mnt/media/potaito/freenas_home/* /media/potaito/freenas_home/

You can also use the file manager to delete/move the files, you'll have to decide yourself which of them to keep.

If you are done, remove the bind mount with

sudo umount /mnt