With glusterfs-3.1.0qa40, the help text for glusterd -f is: -f, --volfile=VOLFILE File to use as VOLUME_FILE [default: /etc/glusterfs/glusterfs.vol or /etc/glusterfs/glusterfsd.vol] However, it appears that glusterd is only looking for /etc/glusterfs/glusterd.vol and not /etc/glusterfs/glusterfs.vol nor /etc/glusterfs/glusterfsd.vol.
PATCH: http://patches.gluster.com/patch/5277 in master (glusterfsd: '-f' option help update)