Thank goodness. btrfs has bitten me way too often on CoreOS. I eventually succumbed to wiping the /var/lib/docker mounted directory on every reboot to minimize the occurrence of the low disk space issues, but nevertheless, issues still exist. Even today, I still have some cases where docker will complain about not being able to create the container/file, due to some inane error. I've had to reboot machines many times just to try to get it to cooperate. Furthermore, that solution of wiping the partition means that my machines need to redownload their docker images on every reboot, which means they come up more slowly than absolutely necessary.