Docker run error: "Thin Pool has free data blocks which is less than minimum required"

Running with data/metadata over loopback devices was the default on older versions of docker. There are problems with this, and newer versions have changed this default. If docker was configured this way, then normal updates (e.g. through rpm/apt) don't change the configuration, which is why a full reinstall was required to fix.

Here's an article with instructions on how to configure older versions to not use loopback devices:http://www.projectatomic.io/blog/2015/06/notes-on-fedora-centos-and-docker-storage-drivers/

You don't have to reinstall Docker. Rather, you can clean up all the containers, images, volumes, etc. under /var/lib/docker directory.

Those images could be pulled up from your Docker repositories again. (This is assuming you only use this Docker host for building Docker images.)

My issue was unrelated to the loopback device problem, but was generating the same error condition. "docker images -a" showed a number of name=none tag=none images taking up space. These images were not "dangling"; they were referenced by a current active image, and could not be deleted.

My solution was to run "docker save" and write the active image to a tar file, delete the active image (which deleted all the child images), then run "docker load -i" from the tar file and create a single new image. No more errors related to Thin Pool space.

Reinstalling docker would have corrected it, simply because reinstalling docker does clear out all images, but it would have begun building up again and then I would have re-encountered this issue in the future.