My situation is that the server I'm running is at least 5 years old and at some point I upgraded from ubuntu 18.04 to ubuntu 20.04. I know you should not touch /var/lib/docker (here just ./) contents but it seems docker has left the ./aufs folder untouched since the upgrade and it using 85G.
Running docker volume ls --format {{.Mountpoint}} it shows only folders in ./volumes nothing in ./aufs. While ./aufs has 85G, there is also a ./overlay2 folder with 25G and the ./volumes folder has only 5G.
I'm confused now. If we should not touch this folder should docker not clean up unused stuff from old installations? I remember that there was an issue after the upgrade that all containers had to be recreated and I think we had to change to overlay2. But why docker reports all volumes in ./volumes and nothing in ./overlay2 then? Can I trust that output, or is it using the data somewhere else?