I was reading that from one person in the Start9 DIY forum. I’m definitely considering it.

Start 9 on initial boot asks which drive to install OS. Then it removes the installation bloat. Next time it boots it asks which drive you want to use for storage. That’s when you can pick your secondary drive.

@npub17kvh...9wn4 is a man that can. I've set up 2. One for btc the other is a server for Nostr, simplex, syncthing etc... I replaced the ssd for a 2tb one and was good

I concur, with @Zaikaboy, I tried to use a PCie M.2 extension and it didn't read from any other M.2s I had beside the one with the OS boot on it.