20.04 – What is filling my root partition?

I have created a new Ubuntu 20.04 VM for my docker host. I then moved my backup over to the new host and restarted all my containers. Apart from docker, docker-compose and ncdu nothing else has been installed on this host.

The VM has a 450GB disk and apparently 340GB are in use. I can not locate what is using all this diskspace though. All docker relevant mounts are in /home/docker/services/. NCDU reports 114.6 GiB disk usage which does not agree with df -h.

So my question is, what is happening here? What is causing this discrepancy?

docker@docker:~$ df -h
Filesystem                         Size  Used Avail Use% Mounted on
udev                                63G     0   63G   0% /dev
tmpfs                               13G  4.0M   13G   1% /run
/dev/mapper/ubuntu--vg-ubuntu--lv  440G  340G   78G  82% /
tmpfs                               63G     0   63G   0% /dev/shm
tmpfs                              5.0M     0  5.0M   0% /run/lock
tmpfs                               63G     0   63G   0% /sys/fs/cgroup
/dev/sda2                          976M  104M  806M  12% /boot
/dev/sdc1                          157G   61M  149G   1% /elastic
/dev/loop0                          55M   55M     0 100% /snap/core18/1880
/dev/sdb1                          1.5T   81G  1.4T   6% /downloads
/dev/loop1                          56M   56M     0 100% /snap/core18/1944
/dev/loop2                          72M   72M     0 100% /snap/lxd/16099
/dev/loop3                          32M   32M     0 100% /snap/snapd/10492
/dev/loop4                          30M   30M     0 100% /snap/snapd/8542
/dev/loop5                          68M   68M     0 100% /snap/lxd/18150
//192.168.178.200/4k_series         79T   66T   13T  85% /4k_series
//192.168.178.200/4k_movies         79T   66T   13T  85% /4k_movies
//192.168.178.200/Docker_Backup     79T   66T   13T  85% /docker_backup
//192.168.178.200/Coding            79T   66T   13T  85% /coding
//192.168.178.200/Music             79T   66T   13T  85% /music
//192.168.178.200/eBooks            79T   66T   13T  85% /ebooks
//192.168.178.200/Cloud             79T   66T   13T  85% /cloud
//192.168.178.200/Movies            79T   66T   13T  84% /movies
//192.168.178.200/Audiobooks        79T   66T   13T  85% /audiobooks
//192.168.178.200/Fred              79T   66T   13T  85% /fred
//192.168.178.200/Series            79T   66T   13T  85% /series
//192.168.178.200/Photos            79T   66T   13T  85% /photos
tmpfs                               13G     0   13G   0% /run/user/1000

NCDU output:

ncdu 1.14.1 ~ Use the arrow keys to navigate, press ? for help                                                                                                    
--- / ------------------------------------------------------------------------------------------------------------------------------------------------------------
   77.6 GiB (##########) /home                                                                                                                                    
   25.9 GiB (###       ) /var
    8.0 GiB (#         )  swap.img
    2.1 GiB (          ) /usr
    1.0 GiB (          ) /snap
  101.0 MiB (          ) /boot
    5.3 MiB (          ) /etc
    3.9 MiB (          ) /run
   60.0 KiB (          ) /tmp
   52.0 KiB (          ) /root
   20.0 KiB (          ) /elastic
   16.0 KiB (          ) /opt
e  16.0 KiB (          ) /lost+found
e   4.0 KiB (          ) /srv
e   4.0 KiB (          ) /mnt
e   4.0 KiB (          ) /media
e   4.0 KiB (          ) /incomplete
e   4.0 KiB (          ) /cdrom
.   0.0   B (          ) /proc
    0.0   B (          ) /sys
    0.0   B (          ) /dev
@   0.0   B (          )  libx32
@   0.0   B (          )  lib64
@   0.0   B (          )  lib32
@   0.0   B (          )  sbin
@   0.0   B (          )  lib
@   0.0   B (          )  bin
<   0.0   B (          )  series
<   0.0   B (          )  photos
<   0.0   B (          )  music
<   0.0   B (          )  movies
<   0.0   B (          )  fred
<   0.0   B (          )  ebooks
<   0.0   B (          )  downloads
<   0.0   B (          )  docker_backup
<   0.0   B (          )  coding
<   0.0   B (          )  cloud
<   0.0   B (          )  audiobooks
<   0.0   B (          )  4k_series
<   0.0   B (          )  4k_movies

 Total disk usage: 114.6 GiB  Apparent size: 128.1 TiB  Items: 4296902  

My fstab:

docker@docker:~$ cat /etc/fstab 
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
# / was on /dev/ubuntu-vg/ubuntu-lv during curtin installation
/dev/disk/by-id/dm-uuid-LVM-2qMn7z44yFIFNUpjG0awRAYnY86pTJbxy0DB3uCLpkalGZFRG023GYBeeazYfbe4 / ext4 defaults 0 0

# Server mounts
//192.168.178.200/Fred /fred cifs credentials=/home/docker/.smbcredentials,iocharset=utf8,gid=1000,uid=1000,file_mode=0777,dir_mode=0777 0 0
//192.168.178.200/Audiobooks /audiobooks cifs credentials=/home/docker/.smbcredentials,iocharset=utf8,gid=1000,uid=1000,file_mode=0777,dir_mode=0777 0 0
//192.168.178.200/Series /series cifs credentials=/home/docker/.smbcredentials,iocharset=utf8,gid=1000,uid=1000,file_mode=0777,dir_mode=0777 0 0
//192.168.178.200/Movies /movies cifs credentials=/home/docker/.smbcredentials,iocharset=utf8,gid=1000,uid=1000,file_mode=0777,dir_mode=0777 0 0
//192.168.178.200/eBooks /ebooks cifs credentials=/home/docker/.smbcredentials,iocharset=utf8,gid=1000,uid=1000,file_mode=0777,dir_mode=0777 0 0
//192.168.178.200/Music /music cifs credentials=/home/docker/.smbcredentials,iocharset=utf8,gid=1000,uid=1000,file_mode=0777,dir_mode=0777 0 0
//192.168.178.200/Coding /coding cifs credentials=/home/docker/.smbcredentials,iocharset=utf8,gid=1000,uid=1000,file_mode=0777,dir_mode=0777 0 0
//192.168.178.200/Docker_Backup /docker_backup cifs credentials=/home/docker/.smbcredentials,iocharset=utf8,gid=1000,uid=1000,file_mode=0777,dir_mode=0777 0 0
//192.168.178.200/Cloud /cloud cifs credentials=/home/docker/.smbcredentials,iocharset=utf8,gid=1000,uid=1000,file_mode=0777,dir_mode=0777 0 0
//192.168.178.200/Photos /photos cifs credentials=/home/docker/.smbcredentials,iocharset=utf8,gid=1000,uid=1000,file_mode=0777,dir_mode=0777 0 0
//192.168.178.200/4k_series /4k_series cifs credentials=/home/docker/.smbcredentials,iocharset=utf8,gid=1000,uid=1000,file_mode=0777,dir_mode=0777 0 0
//192.168.178.200/4k_movies /4k_movies cifs credentials=/home/docker/.smbcredentials,iocharset=utf8,gid=1000,uid=1000,file_mode=0777,dir_mode=0777 0 0


# /boot was on /dev/sda2 during curtin installation

/dev/disk/by-uuid/d47fc774-f9fe-40e8-a185-3a764ce6f971 /boot ext4 defaults 0 0
/swap.img       none    swap    sw      0       0

# secondary mounts
/dev/sdb1 /downloads ext4 defaults 0 0
/dev/sdc1 /elastic ext4 defaults 0 0