Correct me if I'm wrong, but something I would add to this debate is the type
of split brain we are talking about. Glusterfs is quite different from GFS or
OCFS2 in a key way, in that it is an overlay FS that uses locking to control
who writes to the underlying files and how they do it.
It is not a cluster FS the way GFS is a cluster FS. For example if GFS has
split brain, then fencing is the only thing preventing the complete destruction
of all data as both nodes (assuming only two) write to the same disk at the
same time and utterly destroy the filesystem. But glusterfs is passing writes
to EXT3 or whatever, and at worst you get out of date files or lost updates,
not a useless partition that used to have your data...
I think less stringent controls are appropriate in this case, and that GFS / OCFS2 are entirely different animals when it comes to how severe a split brain can be. They MUST be strict about fencing, but with Glusterfs you have a choice about how strict you need it to be.