I don't know zilch about GFS and fencing, but from reading the RHEL
www.redhat.com/docs/manuals/csgfs/admin-guide/ docs and posts here on LQ I get that it is preferrable to have an uneven amount of physical nodes starting at three, and that if you have only two nodes you need to set up a quorum disk to ensure there will always be an uneven number of nodes available to decide which one to fence. Apparently fencing requires hardware. If no fending-capable hardware is available, the RHEL docs may suggest options. Maybe fence_gnbd? Most posts here suggest not to use fence_manual for production devices as it isn't doing any actual fencing, just printing messages humans sh|could react to (as in
errare humanum est :-]). AFAIK running fenced is necesary for even simple GFS. For second opinions please check posts by brianmcgee and druuna and Jeremy's web log. These three I know to have shared GFS information on LQ.
