Mmmm… we might need to see how are organized your partitions.
Which ones are mounted at start :
cat /etc/fstab
Which ones are visible :
( enlarge or maximize your terminal before issuing that command )
lsblk -f | grep -v loop
Which ones are actually used :
df -Th | grep -v loop
ncdu is a folder/file view not a disk/partition usage view.
It helps browsing data with a logical user point of view through files and folders as they are displayed by the system. It’s not for browsing devices, from a physical point of view.
ncdu 1.14.1 ~ Use the arrow keys to navigate, press ? for help
--- / ----------------------------------------------------------------------------------
. 486,0 GiB [##########] /media
7,7 GiB [ ] /usr
. 5,3 GiB [ ] /home
. 4,9 GiB [ ] /snap
. 3,3 GiB [ ] /var
189,9 MiB [ ] /boot
. 12,7 MiB [ ] /etc
. 1,9 MiB [ ] /run
. 144,0 KiB [ ] /tmp
! 16,0 KiB [ ] /lost+found
e 4,0 KiB [ ] /srv
! 4,0 KiB [ ] /root
e 4,0 KiB [ ] /opt
e 4,0 KiB [ ] /mnt
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
Total disk usage: 507,5 GiB Apparent size: 507,4 GiB Items: 1523556
↑ ncdu shows you which folder/files your operating system uses to manage the whole amount of attached data.
Therefore only attached partitions ( = mounted into a folder ) are visible and counted.
Links are shown with an @ at beginning of line, but not counted ( or only once for hard links ).
e at beginning of line is for empty folder.
Full gauge here does not mean 100% capacity but « the heaviest ».