I'm running a 40tb FreeNAS server, I prefer it over something like a QNAP since FreeNAS is way more expandable and feature filled. My hardware is:

Intel Core i3-2100T
Super Micro X9SCL
Fractal Design Node 804 Case
32 gigs DDR3 ECC U-Dimms
2x Dell Perc H310s flashed to IT mode
10x 4tb drives in Raid-z2 (equivalent to Raid6)
1x 240gig SSD as a dedicated SLOG drive for caching data to the NAS

I also have a second NAS with the same hardware I keep at my parents house that I rclone everything to once a month.