I have been running GlusterFS for over 2 years now.
It is stable software, but is known for not playing happy with smaller files if not correctly setup.
Had some fun in the early days tuning the GlusterFS for our environment.
It is important to have your sessions and caches (Including local caching) setup correctly or you may feel the performance impact.
Couple of years old now but Catalyst It have an honest review of the platform on their site. https://www.catalyst-au.net/blog/our-glusterfs-experiences