> What’s the /dev name in your case? In the working case as a CD, it's /dev/sr0. In the non-working case on a USB flash drive, it's /dev/sda and /dev/sda1.
There's a dummy partition in the iso image as well, so I'm not sure why /dev/sda1 doesn't work as well... let's see... When fdisk says that the starting sector is "1", does that mean the first sector (i.e. there's no sector before it) or does that mean the sector after the MBR? On the guix rescue console, I tried comparing the first few bytes of /dev/sda and /dev/sda1 and it seems they are different. That would mean that the ISO filesystem support code can't find the primary volume descriptor any more because it's reading it from the wrong position because it reads from the device file "/dev/sda1" and that file shifts it from where it would have been if it read "/dev/sda". But this "partition?" thing would mean that having a partition table is now mandatory, right? Is that really supposed to be the case? The partition table has a magic mark (0x55 0xAA) in order for it *not* to be mandatory (i.e. if you want to use the whole disk without partitioning anything, go right ahead) and I can still remember using (floppy) disks which had no partition table.