There’s info on github release page for 1.13.1 that says that overlay now replaces devicemapper, details here: https://github.com/docker/docker/releases/tag/v1.13.1
oh, and one more maybe not so obvious thing I noticed (and I didn’t find any explicit info about this scenario) - when I did an upgrade with existing images from 1.12.6 to 1.13.1 devicemapper remained the active storage driver and existing images were available, but if I yum remove docker-engine-1.12 package and do a clean install of docker 1.13.1 overlay driver will be used by default regardless if there were
existing docker images in /var/lib/docker left over from docker 1.12 and those images will not be available (not sure if are actually removed or still taking up space but ‘invisible’) since overlay is now used - tested this on centos 7.
regards,
Mario