Ok, folks,
Here's the answer: making a software RAID on a bare drive with no GPT
works fine. If it has a GPT, and no partition, it fails on reboot, even
with an /etc/mdadm.conf.
I've proved this:
first, I created the array on the bare drive, rebooted, and
/dev/md0 was there;
then, I used parted to create a gpt, then the array, reboot, no
md0, even with mdadm --assemble, even with /etc/mdadm.conf.
finally, I got rid of the disk label (parted to make an msdos
label, the zeroing out the beginning of the disk), and again made
the RAID on the bare drives, reboot, and md0 is there.
So that's what killed me. Admins, take heed....
mark