Docker: Verbrauch Plattenplatz

Das ver­ste­he ich nicht:

root@big:/var/lib/docker# du -sh aufs/ devicemapper/
2.3G    aufs/
29G    devicemapper/
root@big:/var/lib/docker#

Also rund 32 GB in Nut­zung durch Docker, ver­ste­he ich das richtig?
Aber:

root@big:/var/lib/docker# docker system df -v
Images space usage:

REPOSITORY           TAG                 IMAGE ID            CREATED ago         SIZE                SHARED SIZE         UNIQUE SiZE         CONTAINERS
mikesplain/openvas   latest              7806ce6c5043        5 days ago ago      6.082GB             0B                  6.082GB             1
collabora/code       latest              2f454ff26962        2 weeks ago ago     1.556GB             0B                  1.556GB             1

Containers space usage:

CONTAINER ID        IMAGE                COMMAND                  LOCAL VOLUMES       SIZE                CREATED ago         STATUS              NAMES
d6cd523bad74        mikesplain/openvas   "/bin/sh -c /start"      0                   196MB               38 hours ago ago    Up 38 hours         openvas
1d3b8c054653        collabora/code       "/bin/sh -c 'bash st…"   0                   886MB               2 weeks ago ago     Up 38 hours         collabora

Local Volumes space usage:

VOLUME NAME                                                        LINKS               SIZE
e22f15dc716b1c911f51c21c82816c43c992c0ec89cc87481a9608319795b6f3   0                   1.498kB

Build cache usage: 0B

root@big:/var/lib/docker#

Dar­aus lese ich: ca. 7,5 GB Images plus ca. 1,1 GB Container.
Woher kommt die Dif­fe­renz zum obe­ren du?