In researching motherboards I find some that advertise support for RAID. What is the relationship between hardware RAID and FreeNAS? Does FreeNAS require hardware support or can it do RAID entirely in software? If hardware RAID exists will FreeNAS take advantage of it?
Bostjan Cadej's profile photoLesley Longhurst's profile photoJohn Mink's profile photo
FreeNAS supports ZFS. ZFS is software RAID. If you use ZFS, hardware RAID must be disabled.  So my recommendation, use ZFS on FreeNAS with hardware RAID disabled.
My preference is for software RAID, because hardware RAID usually blocks access to the SMART functions that allow the OS to interrogate the drives and run self-tests etc. 
As seems to be the consensus, my understanding is that hardware RAID generally only gets in the way for multiple reasons:

1) ZFS is actually better than standard RAID.  It does more to combat issues like bit-rot and data loss on sectors you aren't actively using as well as the ability to create snapshots for easy backup.

2) Hardware raid is often implemented in a non-ideal scenario, meaning that only that exact (or at least the same manufacture) controller can recover your data when the controller breaks.  This results from actually using a mix of software & hardware in the hardware raid,

3) Hardware RAID requires drivers to play nicely... this is fine, but a pain!

Of course, if your CPU is totally overwhelmed by the overhead for RAID (not unreasonable if you have 20 HDDs...not relevant if you have 4 drives) then you may want to consider implementing hardware RAID...but I strongly recommend looking at reviews to make sure it'll migrate when the card inevitably fails.
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