The Good & Bad Of ZFS + HAMMER File-Systems On BSD
Posted yesterday to the FreeBSD Forums is an interesting thread about ZFS vs. HAMMER, with the original poster providing a lot of his own opinions and since then many other users have jumped in too, which makes for an interesting ready. The ZFS comparison is done to HAMMER1 and not HAMMER2, the next-generation DragonFlyBSD file-system that's still under development by Matthew Dillon.
Among the pros of ZFS are it's self-healing, writable clones, fully journaling system using ZFS snapshots, compression, and portable storage. Among the viewed HAMMER positives are the focus on data integrity, great SQL database performance, lower RAM requirements, supports pseudo file-systems, fully open-source with a BSD license, etc. Of course, with each also comes various cons.
For BSD users interested in comparing HAMMER and ZFS, see this forum thread.