A crucial aspect to Docker is the concept of the copy-on-write layered filesystems. There is a significant amount of documentation on this upstream:
docker-storage-setup is a script to configure the devicemapper or
overlayfs backends, part of the
Project Atomic suite of container
projects. It is run via a systemd service
docker-storage-setup.service before the Docker daemon, ensuring
storage is provisioned according to configuration in
/etc/sysconfig/docker-storage-setup.
You should typically set the contents of that file during system
bootstrap, e.g. in a cloud-init bootcmd: hook, or via
kickstart %post.
Also, in a cloud (OpenStack/AWS/etc.) scenario with the devicemapper
backend, docker-storage-setup can also expand the root volume group
to fill the space allocated for the root disk if GROWPART=true is
set.
For more information on configuration, see man docker-storage-setup.