Hmm, the actual designers and implementers of ZFS disagree with you. Here's their take on hardware RAID controllers and ZFS without a FreeNAS/iX sales pitch: "Hardware RAID controllers should not be used with ZFS. While ZFS will likely be more reliable than other filesystems on Hardware RAID, it will not be as reliable as it would be on its own." They then go on to explain why this is so with a reasonably brief amount of technical detail.