Even mini PCs, which I’m using in a separate testing environment with a few nodes, often perform tasks better than these older servers.

While it might seem tempting to pick up some old server hardware that have advanced features like ECC and SAS drives and all at heavy discounts, Rich Edmonds went down the rabbit hole and warns you against it. Proprietary parts for almost all connections and bays, finding spare parts for dated systems, high power utilization, poor single threaded performance from dated CPUs, noise, and all the other factors outweigh any perceived benefits.