OCFS2 has a couple of nice things going for it. Simplicity, and kernel integration! I actually got it up and running in under 15 minutes on a drbd device, running within two qemu virtual machines. Pretty cool.

http://www.drbd.org/drbd8-howto.html

http://xenamo.sourceforge.net/ar01s03.html#id2477161

http://www.rampant-books.com/art_hunter_rac_oracle_o2cb_cluster_service.htm

Unrelated:

http://zhenhuiliang.blogspot.com/2006/04/csync2-is-so-cool.html