I am trying to upgrade from F18 to F19 with fedup 0.7.3.4.fc18. Many people are reporting problems when trying to use fedup with software RAID systems. Some suggested adding /etc/mdadm.conf to the image so I tried to do this myself. I found that it is no longer compressed with gzip, but xz. However, when I tried to decompress it, it would fail at 99%. I checked the end of the image file and found two uncompressed cpio archives. One already contained /etc/mdadm.conf. The other contained /usr/lib/dracut/hooks/pre-pivot/99-keep-initramfs.sh, as found in /etc/fedup/update.img.d. These are both appended by fedup. I'm not an expert on initramfs but I don't think appending uncompressed archives to the end of a compressed archive is going to work. fedup certainly didn't boot up for me and I could see no sign of /etc/mdadm.conf. lsinitrd doesn't show it either. I suppose the image needs to be downloaded, decompressed, appended to, and then recompressed. It is easy to see the uncompressed files at the end, just view /boot/initramfs-fedup.img with less and hit the end key.
No, it works fine. The kernel initramfs code specifically allows for concatenated images. Try it and see. Boot with 'rd.break'; you'll see that the appended files are present in the initramfs.
Turns out I was hitting bug #970580. Sorry for the noise and thanks for the info.