Server drops to dracut debug shell after upgrading from Fedora 14 to 15

I have just upgraded to Fedora 15 using PreUpgrade. In particular, I did

sudo yum update
sudo yum install preupgrade
sudo preupgrade-cli "Fedora 15 (Lovelock)"

When it told me to do so, I have entered:

sudo reboot

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and the waited for the upgrade to complete. My server now fails to reboot, dropping to the debug shell:

dropping to debug shell
sh: can't access tty; job control turned off
dracut:/# _

Typing in 'dmesg' gives me the following information (I have omitted everything but the last two lines):

[  8.574475] dracut: Autoassembling MD Raid
[ 29.531556] dracut Warning: No root device "block:/dev/disk/by-uuid/812eb062-d765-4065-be34-4a2cf4160064" found

The system is installed on two S-ATAII HDs (Raid 1) and I can boot into the system by choosing the old Fedora 14 kernel (2.6.35.14-95.fc14.x86_64) in Grub.

The output of 'cat /proc/mdstat' (Fedora 14) is:

Personalities : [raid1] 
md127 : active raid1 sda[1] sdb[0]
  1953511424 blocks super external:/md0/0 [2/2] [UU]
  [>....................]  resync =  4.6% (91244352/1953511556) finish=342.4min speed=90630K/sec

md0 : inactive sdb[1](S) sda[0](S)
  4514 blocks super external:imsm

unused devices: <none>

Can anyone give me a hint on how to fix the problem, namely how to make my machine boot the Fedora 15 kernel?

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I'd check what options you're passing to the kernel from grub. Specifically, what's the root= string on each of your kernel choices?

You can check what the UUID should be by typing:

mdadm --examine /dev/sda1

(This should work from the dracut shell, if it doesn't, maybe you need to rebuild your initrd first?)

You can also try passing the md device name as the kernel boot option, so change the grub option to something along the lines of:

kernel vmlinuz-2.6.42 ro root=/dev/md127

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Not sure if you have fixed this yet, but I have ran into the same issue. Looks like this site has some great places to start looking at:

http://fedoraproject.org/wiki/Bugs/Common

In general, the one that seems to be effecting both of us is the one about hardware RAID1 configurations.

http://fedoraproject.org/wiki/Bugs/Common#Boot_sometimes_fails_when_installing_to_a_pre-existing_partition_layout_with_complex_boot_configuration_.28e.g._software_or_firmware_RAID-1.29

Looks like an oopsie that essentially requires a reinstall from scratch (including resizing partitions) using Fedora 16.

Hope this helps!