What for?
Stuff like that pops up all the time, but CMs aren’t exactly cheap. They are great if you need a tiny form factor custom device, but they aren’t cost effective in regards to performance at all.
A regular small form factor PC with an i7 or comparable AMD CPU will beat that CM cluster on price, performance, maintainability, and ease of use every time.
What for?
I think this fairly often when I see some of the things that have been created for RPi hardware. Some things are cool, but most fall into the category of “it’s cool that this exists”, but doesn’t really have a purpose beyond that.
IDK a practical use for a 7-pi cluster, but I will note, for tasks that can be performed within the pi’s performance envelope, it’s an incredibly power-efficient system. So while in many cases a few raspberry pi may lose on upfront cost, their performance/dollar tends to even out when you start factoring in energy costs.
There’s diminishing returns as you start to get towards the upper end of performance though, and IDK how 7 pis at full load compare in W/flop vs a SFF PC. 28 cores @2.4 GHz, 35 W for the pi, vs a new CPU running 8 cores, @4.7 GHz, 120W may be a close race.
There’s more nuance than just cores & frequency when it comes to performance in a given task, but the pi is remarkably lean.
