40 HDD is a lot.
Check out 45 Drives. They have a homelab focused offering that has 15 bays https://45homelab.com/#product
To get 40 hard drives, you’d be looking at something like their Storinator S45 https://www.45drives.com/products/storinator-s45-configurations.php
Nice work! Always satisfying to see an idea reach the real world
Both machines are on display at a museum in Germany. Volunteers have iterated on MMX to the point where is can play music https://www.smmk.de/marble-machines.html
Where are the external drives living? Hard drive make their own noise. Might consider going with solid state if you want silence.
One example of this that’s making the rounds: https://www.asustor.com/en/product/FS67
Just discovered these when I asked Mastodon what OS I should use for a PC I’m building with my kid. Looking forward to trying them out!
https://hachyderm.io/@PeterBronez/112496363400912617