mdadm raid1 confuses fedora 21?

[Tom Horsley]

I enabled mdmonitor, and created a raid1 while booted
into fedora 20 and everything is wonderful. It recognizes
the entry in fstab and boots no problem. (I'm not
using the raid1 to boot from, BTY, just as a data disk).

I then tried to boot the fedora 21 partition on the
same machine (being sure to enable mdmonitor in it
as well), and it never finishes booting. (Though
a fedora 21 live USB stick boots fine).

Has something changed in the vicinity of mdadm
in f21? Do I need the initramfs rebuilt or
something?

Right now it stops booting with messages on the
screen something like "/dev/sde is a large
disk, trying to use READCAPACITY" and just
sits there. (Where /dev/sde is one of the two
disks I have in the array).