Thanks for that Jason,
Overlay2 seems to be what I am using.
sudo ls -l /var/lib/docker/
total 64
drwx------ 16 root root 4096 Apr 8 05:13 containers
drwx------ 3 root root 4096 Apr 7 11:41 image
drwxr-x--- 3 root root 4096 Apr 7 11:41 network
drwx------ 269 root root 28672 Apr 8 05:13 overlay2
drwx------ 4 root root 4096 Apr 7 11:41 plugins
drwx------ 2 root root 4096 Apr 7 11:41 swarm
drwx------ 2 root root 4096 Apr 8 05:03 tmp
drwx------ 2 root root 4096 Apr 7 11:41 trust
drwx------ 7 root root 4096 Apr 8 05:13 volumes
ubuntu@docker-vm-0:~$ sudo ls -l /var/lib/docker/overlay2
total 1088
drwx------ 5 root root 4096 Apr 7 11:47 018b82cd15470d1ee0cba21290ec84c8f2c3d75985815d7d2a81499585f08cd5
drwx------ 5 root root 4096 Apr 7 11:46 04c22cc4052327a70c4b95a16daff0fea0e3a14a5943bbf908a1643fb9e58e87
drwx------ 5 root root 4096 Apr 7 19:13 05e8f3b217c83a32e3070e6b39ca66dd3360ff77d6fe121d032a387ee09ae351
I will monitor the bug and hope for a quick fix.
Thanks
Mathias