Bug#640655: grub-pc: grub won't boot if installed on a degraded raid1 array (with missing disk)

[Stephane Chazelas]

Package: grub-pc
Version: 1.99-11
Severity: normal

Dear Maintainer,

If setting up a machine (virtual for instance) with a RAID1
array initially created degraded with a missing part, then grub
won't boot (reboots after "loading grub"):

Example:
(I don't think the LVM part is relevant)

truncate -s10G file
losetup /dev/loop0 file
mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/loop0 missing --metadata=0.9
sfdisk /dev/md0 << E
# partition table of /dev/md0
unit: sectors

/dev/md0p1 : start=     2048, size=  2097152, Id=83
/dev/md0p2 : start=  2099200, size= 18872192, Id=8e
/dev/md0p3 : start=        0, size=        0, Id= 0
/dev/md0p4 : start=        0, size=        0, Id= 0
E
mkfs.ext3 /dev/md0p1
pvcreate /dev/md0p2
vgcreate test /dev/md0p2
lvcreate -L4G -n root test
mkfs.ext4 /dev/root/test
mount /dev/root/test /mnt
mkdir /mnt/boot
mount /dev/md0p1 /mnt/boot
debootstrap --arch amd64 sid /mnt http://ftp.se.debian.org/debian/

setup /dev, /sys, /dev/pts, /proc
edit fstab, passwd root...
Then install linux-image, mdadm, lvm2, grub-pc...

grub-install /dev/md0

vgchange -an test
mdadm --stop /dev/md0

and boot /dev/loop0 with kvm, the machine automatically reboots
with (from memory)

Loading grub_1.5...

Loading grub

If I add a second disk to the array, then it boots OK. Initially
reproduced with a real machine.

-- 
Stephane