I have the possibility of getting my hands on a practically unlimited supply of S905X2 Android boxes, they have 2GB of RAM and 8GB eMMC, only 100Mbit LAN but USB-3 as well.
I was joking around with colleagues, what about making an ARM cluster out of them? Use the 100Mbps port as a management port and add a USB3 Gigabit or 2.5G adapter for general traffic. Power the cluster by PoE using PoE to 5v splitters from a smart, management switch with PoE (10W each box?).
Lets say I got 40 boxes with 4 cores, that’s 160 cores and 80GB of RAM. It could run Armbian with Kubernetes or something lighter. I personally have no use for it, but it could be a fun proof of concept?
Tell me why I shouldn’t do this! Tell me why it won’t work and why I’d be wasting my time.
Not only a ton of work but likely also much more expensive than you might think even with free boxes. A Gbit USB adapter costs lie $10, you might also need a cable, a switch, maybe (some) PSUs, a power strip, maybe some box to put everything into… And now you suddenly are spending $400-800 on this project just to get a rather lame cluster. Those cores are rater slow, 2GB of RAM is not that much, and 8GB of storage means you also need some kind of NAS.
If you like the project go for it but do not expect this to be a wise way to spend your time and money. 3-4 NUCs are likely less expensive and much more fun.
£5 for a USB NIC - £100 £3 for a PoE to 5V DC splitter - £60 £2 in short cables - £40 Shelf? £20-50
PoE Switch I already have spare Leaf switch I already have spare Network storage I have in abundance.
Cost wise it’s not prohibitive, about £250
I think the biggest worry is, as you say, it might not be the most stable or impressive compute.
£5 x 40 = 200. £3 x 40 = 120. Seems like you calculated with 20 and not 40. This helps to bring the cost down but even for 250 you can at least a single decent NUC.
Plus the entire thing would likely be pulling way more power too, and take up 10-20x the space.
I switched a 6 year server over to a 3 node pi k8s and it runs with half the power. The one annoying thing is building images for Arm arch as a lot of common helm charts aren’t built for multi arch builds yet.