My setup is a bit weird now; I have some cases that holster the drives [0], with a low-wattage ATX power supply that exists solely to power the drives. I a bunch of sata male-to-female cables on the case [1], and then a bunch of USB3 to SATA adapters plugged into a couple USB3 hubs into my leader Jetson. I have ZFS On Linux set up on there, and have an NFS share set up on the ZFS mount.
I use Kubernetes to distribute my projects across the cluster, and use NFS for any kind of shared data. It works way better than one might think.
[0] https://www.ebay.com/itm/4-Bay-USB3-0-2-5-HDD-SATA-Hard-Driv... [1] https://www.ebay.com/itm/HDD-SATA-Male-to-SATA-Female-cables...
EDIT: Just a note, if you decide for some reason to copy my design, I'm flattered; make sure you either get an ATX power supply that's extremely low wattage or is smart enough to lower the wattage based on load. I made the mistake of taking a power supply out of an old gaming rig the first time I did this, and it ended up consistently using 600W all the time, leading to a hefty power bill one month. I was able to find a power supply that peaked at 200W on ebay for ten bucks, and seems to idle at around 50W, which is much more manageable.
That said, if anyone is looking to stay within the x86/x64 family of CPUs, I actually recommend looking for a used Wyse/Dell thin client on eBay. You can often get a decent quad-core system with USB3.0 and 4-8gb of RAM for around a hundred USD.
When I was using it, I ended up not using the built-in SATA port and instead just using it as yet-another-node in my cluster of ODroid XU4s