@agowa338 from a long line of failed sata and sas controllers and failed motherboards, failed drives, some running unraid - technically RAID4, I recommend only RAiD10. And not using some nas software - too much overhead for what is access to nfs and iscsi.
Also, how will you back it up? Even if, somehow, a 10 GigE backbone gets setup, 20TB is still almost 24 hrs if not more. Adding in NAS layers means taking longer.
Having spent a few decades with hardware NAS's and HA based glusterfs, keep it simple and document how to recover when it blows up and all data disappears due to some raid glitch, os fault (lvm metadata corruption), ecc errors, multiple drive or controller port fail. It will happen.