Where is the space available on my SD?

[Nachteule]

Hmmm, please show me the output of sudo btrfs filesystem df /

Terminal

sudo btrfs filesystem df /
Data, single: total=6.22GiB, used=3.43GiB
System, DUP: total=32.00MiB, used=4.00KiB
System, single: total=4.00MiB, used=0.00B
Metadata, DUP: total=439.00MiB, used=220.03MiB
Metadata, single: total=8.00MiB, used=0.00B
GlobalReserve, single: total=76.00MiB, used=0.00B

That's my output of a 2.5 year old rpi1 installation (7.2G root partition)

and sudo du -d 1 -h --exclude="/proc" --exclude="/sys" --exclude="/dev" /
could be helpful

Terminal

sudo du -d 1 -h --exclude="/proc" --exclude="/sys" --exclude="/dev" /
8,6M /bin
51M /boot
7,5M /etc
650M /home
167M /lib
0 /media
7,2M /opt
72K /root
356K /run
15M /sbin
0 /srv
4,0K /tmp
606M /usr
124M /var
0 /xbmc-backup
0 /net
0 /mnt
0 /selinux
1,6G /