* The controller's firmware is an additional layer of complexity that cannot be inspected by arbitrary third parties. The ZFS source code is open source and can be inspected by anyone.
One might to try using single-drive RAID 0 arrays to try to use a RAID controller like a HBA, but this is not recommended for many of the reasons listed for other hardware RAID types. It is best to use a HBA instead of a RAID controller, for both performance and reliability.
= Hard drives =