So FreeNAS as we know it will merge or ‘unify’ into TrueNAS later this year. I think this is going to be very interesting, looking forward to testing TrueNAS v12 nightlies due on 11th March. 
https://www.ixsystems.com/blog/freenas-truenas-unification/
Still no dual controllers… That is the one feature that would change the industry!
What do you mean by dual controller specifically?
Dual controllers allow high availability of your NAS. If one controller fails, the other takes over immediately.
How is that connected electrically to the drives? Could you send me a link with details of such a dual controller setup?
Every enterprise storage company I know of supports this. You can take a look at the solutions from NetApp, EMC, HPE, or Pure. Essentially they use SAS for drive access since it supports two uplinks to the drives.