I have zero experience with debian, but on several other distributions I
have noted that an upgrade to a very recent kernel from a fairly old
kernel (which you did) will make the LVM not work if you're using that.

	By "that", you mean LVM?  No, straight MD RAID 1.

If not, forget I said it, it's not related and I never chased it, I just
saw it a few times and muttered mighty oaths and moved on.

	Oh, it's almost surely related to the new version of udev.  John
Robinson's response makes it clear udev is assigning a different block
device (sdx vs mdx), whihc is probably why it's failing.  I did try
different targets, and /dev/hda and /dev/hdb definitely do not exist.  I'll
look for sda and sdb when I get the chance.  'Should be an easy fix if
that's all it is.