And to make it really overkill and reliable, duplicate this physical installation twice more and setup DRBD and Pacemaker for an extremely HA filesystem with Quorum.

This is all part of why I dislike unRAID. Not only do they offer literally nothing that I can tell of value, but they act like a bunch of normal features are special. They pretend that they are doing something special with KVM and Docker and RAID 4 - all things that you already have in equal or superior form, for free, with an enterprise Linux distro. Install Fedora for free, and you have a simpler, safer, more powerful alternative to unRAID that is only upsides, I think. More power, less effort, less cost, easier to support, easier to get support.