I looked into GlusterFS at one point. GlusterFS is a no-go for static file serving in hostile environments. It asks every node to look for a file, even if it's not there. You can imagine the DDoS attacks you could build here using a bunch of 404 requests for files that don't exist.

One story I heard from a PHP dev is that it would take 30 seconds to load a page while it looked for all the files needed to run it.

Yea, GlusterFS is terrible at PHP, or anything involving lots of small files. Like, static sites or say git repos.

I don't know if it has been considered, however we do have a strong pattern for using DRDB.