data-only container?

[quantombone]

The online example I see which talk about data-only containers, have Docker files that look like:

FROM ubuntu:14.04
VOLUME /var/lib/mysql
CMD ["true"]

See http://howchoo.com/g/zdq5m2exmze/docker-persistence-with-a-data-only-container

So I'm curious if the mkdir command makes this a non "data-only container"
data-only containers are not supposed to take up space, see http://container42.com/2014/11/18/data-only-container-madness/