Currently using Unraid. I like the docker management, plugin support, and the flexibility with adding storage. But I do already have a lifetime license that I got for cheap a few years back. They’ve raised the price significantly since then
If I had to choose today, I’d go with TrueNAS Scale
They are probably 256gb drives that show up in the OS as 4tb. When you start writing files over the actual capacity of the drive , it will just start overwriting the initial files that you put on there.
Good thing Amazon has a good return policy