I installed a raid1 on a debian lenny box with only 1 drive "--raid-devices=1" because I didn't have the other drive yet. When I got the other drive, I used "mdadm --grow /dev/md0 --raid-devices=2" and "mdadm --manage /dev/md0 --add /dev/sdb1" The original drive is sda1. I watched /proc/mdstat until it was completely synced, and after a reboot, the system will not reassamble the raid. It fails with "mdadm: no devices found for /dev/md0" This is where root is, therefore, I get nowhere. From a rescue cd I can disable the other drive and shrink back down to 1 device and it boots fine. Any help is greatly appreciated. Thanks.

I would check /etc/mdadm/mdadm.conf, maybe run update-initramfs after growing the array before rebooting. Not a sure shot tho.