Presence of this README indicates that an unmaintained version of Gluster was enabled on this system. The centos-release-gluster-legacy package caused the removal of centos-release-gluster* versions that do not receive updates anymore. It is strongly recommended to follow the releases for Gluster deployments and plan for upgrades accordingly. An announcement is sent to the CentOS Announce and Gluster Announce mailinglists when a new version becomes available. More details about the versions and their End-Of-Life dates are on https://www.gluster.org/community/release-schedule