Miles better than all that geom_xxx RAIDs (I've been maintainer of geom_raid5, mind you), chipset RAIDs and FFS2 SU+J stuff, which is not completely stable even right now — I've got a ton of erros from forced foreground fsck after "normal" background fsck completion as soon as 2019 (I don't have single R/W FFS2 after that, and I'm happy!)
With all my due respect to McKusick, all this modernization of FFS2 (SU, snapshots, SU+J) always was very fragile, and software RAIDs implemented as GEOMs is much worse than ZFS VDEV layer.
Linux-induced changes downgrade ZFS performance a lot, though :-( Another level of indirection in ARC is really big deal.
