Total correction on this… Original with some corrections left below to explain confusion:
Prior to experimenting with an instance I got a snapshot. This is an ephemeral instance with an extra 3GB of volume-backed storage. The problem is that the snapshot only got the 3GB, not the full 80 or 83. So when I tried to rebuild from what I thought was a full image, it failed. What still confuses me is why the snapshot shows 0 bytes. The only thing I could think of is that this is 0 bytes “of my 100GB allocation”, because snapshots on ephemeral instances don’t eat into our allocation. So maybe it’s just not seeing the actual size because it’s getting that data from the wrong place.
Whatevah. I’m going to blow away that instance, and the snapshot image, and the extra 3GB volume, and try this again. I’m sure I messed up somewhere.