how do i boot when one of the disks in raid 1 / partition fails?

[Tomoki Taniguchi]

I have installed feisty 7.04 server
on a box with 2 identical SATA devices.

i have setup 2 raid1 partitions using mdadm.

/ consists of /dev/sda1 and /dev/sdb1
swap consists of /dev/sda5 and /dev/sda5

the system boots fine.
and i have also installed grub on both drives mbr so that
the system can still boot even if the main drive fails.

to test what happens when one of the disks fail,
i shut down the system.  removed one of the SATA cables and
started the system up.  But the boot process fails
because it can't seem to find md0.

how do i get it so that ubuntu continues to boot even if
one of the drives in the raid1 fails?

TIA,
Tomoki