I use a small SoC (X10SBA from supermicro) in a mini-ITX case that fits 6 HDD drives (currently 3x3TB raid6) running Arch Linux. The Intel celeron J1900 is more than up to the task, and you get a low powered device with which you can serve a website, have a NAS, media center, headless server, syncthing, etc. Great experience so far and quite inexpensive device that runs 24/7.