It looks like there’s a little glitch when moving RootFS to an external USB drive: if I do this from a 2 GB SD card, it fails while trying to create 1.8G swap file lthough I disabled swap), whereas it works ok when doing this with a 4 GB SD card.
This is with DietPi 6.8, and just FYI - I’m fine with using the larger card, although in this case a truly minimal / old / slow SD card would be nice to use for this scenario, as it only needs to go through the power-up boot sequence.
-jcw