Follow up #1:

Seems like I'm getting the "bd_claim" error in md. Even on a fresh boot
after doing the fdisk, I'm still getting errors that /dev/hda1 is in
use. AFAIK, nothing should have touched the disks yet if I go straight
into creating the md[0-3] nodes and using mdadm to create the raid sets.

Old config:

Pri/M: 72GB HD
Pri/S: 80GB HD (removed this drive)
Sec/M: 72GB HD
Sec/S: CD-ROM

Even moving the 80GB slave off of that IDE chain doesn't fix the issue
with /dev/hda1 being in use.

Since I'm also seeing spurious error messages from mdamd about /dev/hda1
having a file system on it, I'm nuking the drives using Darik's Boot and
Nuke. Maybe the Gentoo 2005.0 Universal CD is attempting to mount
partitions that it thinks it understands.

Other things under consideration:

- it's an older motherboard (Gigabyte GA-6VA7+), maybe there's a bug in
the IDE chipset (or a setting that I've missed in the BIOS)

- user error... I thought I understood what's going on, but maybe I don't

- might try the 2004.0 CD again, since I know that worked last year