Every time we hear that hardware RAID "might" or "could" do something, this is also marketing.We could compress all that to "If you choose hardware RAID over ZFS RAID, you'll be using hardware RAID instead of ZFS RAID." It's a redundant point that is simply worded in such a way as to make it sound as if we obviously want one thing and not the other, but doesn't actually say that. This isn't a warning, it's just restating the original decision again. Of course it can't, because we are asking the RAID hardware to do that. That ZFS won't be able to "balance reads and writes" and such is, again, marketing.It's equally designed for both, this is really just marketing fluff. That FreeNAS is "designed to use its own volume manager" is totally fine, but FreeNAS is just FreeBSD with a web GUI and FreeBSD was also designed to be used on hardware RAID and do whatever you need it to do.The information here makes some assumptions that make sense, given that this is a FreeNAS resource, but carrying this implication to other ZFS scenarios makes no sense. But let's break this down to be sure we understand why this is a vendor trying to make a sale and not engineers giving you valid information. In its latest version, the older statements have been moved from true to now quite misleading and clearly an open attempt at marketing.
This was then combined with the "Chinese telephone" effect of people in an insular community repeating this misinformation second or third hand until it became lore and was then eventually believed even though obvious information and common sense would tell us it is not possibly true. So where does this myth come from? Well, from what we can tell, it comes from one true, but marketing style statement from the FreeNAS folks that was worded correctly but in such a way that people who made false assumptions and added their own implications to the statement taking something true and making it very, very untrue.
ZFS is used on top of hardware and software RAID in most cases, this is the standard deployment of it outside of massive Sparc architecture mini computers because anything that runs ZFS (FreeBSD, Ubuntu or Sparc AMD64) would all be expected to be VMs and not on bare metal, so ZFS' primary use and role is on top of other RAID.Any working filesystem will work on any of these by definition.
This abstraction and interface system is universal and total. Hardware RAID, or Software RAID, or LVM, or whatever present a " drive appearance" to upper layers.