[How to do instruction] Boot USB. Move sd-card to USB Drive

[TheOldPresbyope]

Nicely done.

To add a little technical meat to the bone (USB mass storage boot documentation):

• The Raspberry Pi 2B v1.2, 3A+, 3B, and Compute Module 3 all require a specific One-Time Programming bit be permanently set before they can boot from USB mass storage. The state of this bit is checked and can be set via moOde's System Config screen. This is an irreversible action.
  
• The Raspberry Pi 3B+ and Compute Module 3+ support USB mass storage boot out of the box. (My only 3B+ is packed away ATM but I believe this just means that OTP bit is already set.)
  
  

The Raspberry Pi 4B is fundamentally different under the covers from its predecessors. It has less boot code in its microcode and requires the newer firmware referenced in Drone7's post in order to boot from USB mass storage. The OTP-bit test does not apply. Everything in Drone7's post down to "While your MoOde micro-sdcard is removed from your Pi..." deals with this firmware issue.

So, in response to that final "YMMV", booting from a USB mass storage device works fine with RPi 2B v1.2, 3A+, 3B, CM3, 3B+, CM3+ provided the OTP bit has been set first.

I've been booting moOde on a 3B+ from a USB thumbdrive for some time now. Disk activity is slower than if I used a uSD card but it is much more convenient because of the enclosure this particular RPi is in (it's a SmartiPi Touch 2 screen and case). As Drone7 notes, it would be the reverse with an RPi4B and a USB 3 thumbdrive plugged into one of the USB3 ports.

Regards,
Kent