I was thinking that a ZFS raidz2 setup on essentially 6x 4TB drives (4x 4TB and 2x 6TB drives that have been partitioned so that I can use the extra space elsewhere). Link to my forum post on what OS to choose. I'm planning to setup a Linux server for running Plex. I have no experience with Fedora Server, so I cannot comment on how well that works. That being said, Ubuntu server is very stable and works very well, and if you're comfortable with the command line enough to setup RAID Z2, it will have better software support and functionality at the cost of ease of use. You do lose the ability to run docker containers unless you run a VM dedicated to docker, but it's easy enough to do if you need that functionality. If you want to run ZFS (highly recommended, especially if you have a lot of drives), TrueNAS is the way that requires no command line input. It's very easy to setup and pretty darn stable. The way I have my server setup is TrueNAS (the rebranded name of FreeNAS) to run my NAS and plex server with an Ubuntu Server VM running services that do not work on FreeBSD. I'm thinking that ZFS raidz2 is my way to go and not sure which features are best with Plex and which OS offers better compatibility and ease of updates. I have little experience with Ubuntu and no experience in the others or much of any Linux systems. Looking through articles and forum posts, I'm thinking the best options for OS are Ubuntu Server, Fedora Server or maybe FreeNAS. With 2012 R2 end of life and security patches and the cost of Windows OS licensing (I cheap out 'save as much money' as often as possible), Linux is looking like a great option as plex was in Linux, Linux can be smaller in required space and is still less commonly used (hopefully less commonly sought to exploit). I already have a Plex Media Server (PMS) setup on a Windows 2012 R2 server.

Configure plex media server windows