That was one of the alternatives I was exploring also, except not GlusterFS but CEPH (because GlusterFS seems to eat up CPU a lot) and CEPH is more capable of doing larger shares and more I/O working than GlusterFS.
We also have a Rancher setup running, just for testing and there we tried OpenEBS. Although it looked very promising, it’s a hell and pain to get a storage layer working in a K8s environment.
I might also check if OpenEBS or a different one could work for Docker swarm clusters.