A recent thread on the FreeBSD -current mailing list discussed the stability of ZFS on FreeBSD. Scott Long noted that ZFS requires proper tuning to be stable:
"I guess what makes me mad about ZFS is that it's all-or-nothing; either it works, or it crashes. It doesn't automatically recognize limits and make adjustments or sacrifices when it reaches those limits, it just crashes. Wanting multiple gigabytes of RAM for caching in order to optimize performance is great, but crashing when it doesn't get those multiple gigabytes of RAM is not so great, and it leaves a bad taste in my mouth about ZFS in general."
ZFS was committed in April of 2007 by Pawel Dawidek who notes that he is using ZFS quite successfully on all of his systems. He then cautioned, "of course all this doesn't mean ZFS works great on FreeBSD. No. It is still an experimental feature." In response to some negative comments about ZFS on FreeBSD, Pawel noted, "in my opinion people are panicing in this thread much more than ZFS:) Let try to think how we can warn people clearly about proper tunning and what proper tunning actually means. I think we should advise increasing KVA_PAGES on i386 and not only vm.kmem_size. We could also warn that running ZFS on 32bit systems is not generally recommended."
"The universal need for tuning combined with the poorly understood problem reports tells me that administrators considering ZFS should expect to spend a fair amount of timing testing and tuning. Don't expect it to work out of the box for your situation."