I ran into an issue where despite the presence of the _netdev option in my fstab file, my GlusterFS mount point was failing to mount on system start.
There is a log in /var/log/glusterfs/ that pretty clearly showed it was trying to start before networking had started, as it kept failing on name resolution for whatever node I used in /etc/fstab.
Poking around a bit I found someone with the same problem on Server Fault. He had discovered a further log, in /var/log/upstart/ that showed an error message generated from the upstart script /etc/init/mounting-glusterfs.conf.
A little more reading showed that mounting-glusterfs.conf relies on another upstart job, /etc/init/wait-for-state.conf. This was the last clue I needed - as wait-for-state.conf expects a job name passed in as WAIT_FOR, not an event as mounting-glusterfs.conf tries to use.
So I changed WAIT_FOR in mounting-glusterfs.conf to networking instead of static-network-up and that resolved the issue.
Perhaps the wait-for-state.conf script has an updated version, as it seems some people are saying that mounting-glusterfs.conf works on other distros. So that might be a solution as well. But the change above is working for me on Ubuntu 14.04.