I have a running docker service in a Fedora 21 system for a while. Recently I got some disgusting erros preventing restart docker:

device-mapper: table: 253:7: thin: Couldn't open thin
internal device 

I am a docker newbie so I lost a lot of time thinking if my thin device got corrupt or whatever. Indeed I openened an issue (#16341) to the docker project to report it. But now I conclude is not an upstream error but a Fedora's packaging one.

The problem was caused in this regular update:

which did this:
+DOCKER_STORAGE_OPTIONS=--storage-driver devicemapper --storage-opt
-dm.fs=xfs --storage-opt dm.thinpooldev=/dev/mapper/vg_patxuko-docker--pool

And after the next system reboot the docker service was unable to restart. Removing the DOCKER_STORAGE_OPTIONS value returned system to service.

More details at this comment.

Hope it helps