A simple system with two software raid 1 devices running fedora 21. fedup --network 22 upgrade successfully finished. However, the system would not reboot. It complained that /dev/md0 was not found. Upon examining, the /boot/grub2.cfg file was found to contain the wrong UUID for the /dev/md0, the software RAID that was in place. After booting from live USB, and learning the correct name from mdadm --examine --export , the grub file was updated manually and the system booted correctly.
correction: mdadm --detail --export was the command.
Yeah, this is one of the many problems that arises from trying to use a generic upgrade.img to boot everyone's systems - config files that get put into your initramfs are missing from upgrade.img, so the system doesn't always get set up correctly. Since fedup is deprecated and has been replaced with dnf-plugin-system-upgrade in F21 and later, and dnf-plugin-system-upgrade doesn't use upgrade.img, this shouldn't be a problem anymore. It sounds like you got your system upgraded already, but if anyone else hits this problem I'd suggest they use `dnf system-upgrade` instead.