Check your /etc/default/grub, if you use raid 1.

Sun Jul 29 16:56:57 UTC 2012

On Sun, Jul 29, 2012 at 11:23:51 -0400,
   Sam Varshavchik <mrsam at courier-mta.com> wrote:
>
>I think I remember seeing someone reporting the array assembly bug 
>when it's not enumerated in rd.md.uuid, but I can't find the bug 
>right now.
>

I found two related bugs. The second is listed as closed.

mdadm raid10 incremental assembly fails at boot, creating a degraded array:
https://bugzilla.redhat.com/show_bug.cgi?id=823597

make mdadm --add not do stupid things:
https://bugzilla.redhat.com/show_bug.cgi?id=808774