06-17-2020, 09:58 AM
It may be better to dd the mmc device to a .img file rather than to a raw device, as the geometry may differ enough to throw it off when you dd it back to the mmc. Back up that .img file, and use it to restore the mmc later. If you have the extra hardware, you might want to test this on another board like a RPi or a x86 system to make sure you can reproduce it successfully. With that said, this is the method I've used for years to make backups of my RPi installations both for cloning and for restoring after a SD card failure (commonplace in the first few Pi models).