I'm installing Arch on a new machine, coming from a long Linux (recently Gentoo) background. I've followed both the RAID/LVM howto and astrocrep's post (http://bbs.archlinux.org/viewtopic.php?t=28046). I think I'm following every step, even including rebuilding the initrd with mkinitcpio -g ..., but it still fails to mount my root filesystem (md3). I see the raid autodetect work and build md3 just before the kernel panic failing to mount it.
If I boot with an initrd of kernel26-fallback.img, then I can boot fine.
Relevant mkinitcpio.conf lines:
MODULES="pata_amd ata_generic sata_nv"
HOOKS="base udev autodetect pata scsi sata raid keymap filesystems"
Relevant /boot/grub/menu.lst lines:
title Arch Linux [/boot/vmlinuz]
kernel /vmlinuz26 root=/dev/md3 ro md=3,/dev/sda3,/dev/sdb3
I did try kernel26.img, but I also dumped my own mkinitcpio into initrd26.img, so that is a valid line. Neither my own initrd or kernel did it (thought kernel26-fallback did).