problems booting from software raid

[Franz Waldmüller]

Hi,

I am using a software raid 1 build with mdadm upon the installation of 
ubuntu 10.04.

Now I wanted to exchange one harddisk with another one. I copied the 
partition table from one hard disk to the new one:

# sfdisk -d /dev/sda > sfdisk /dev/sdb

Then I added every partition as a spare device to the corresponding raid 
device. This worked fine so far.
Then I executed
# dpkg-reconfigure grub-pc
To write the boot loader to all hard disks.

I rebooted the pc, unplugged one hard disk and adjusted the boot order.
The PC does not boot.

I installed grub to all hard disks seperately updated the intramfs 
manually but nothing works. The Bios does not show an error message it 
just reboots again at the point when the operating system should start.

I tried all possible bios configuration concerning the boot order of the 
hard disks. with no effect.

the boot degraded option is set to yes (dpkg-reconfigure mdadm)

/etc/mdadm/mdadm.conf:
# definitions of existing MD arrays
ARRAY /dev/md0 level=raid1 num-devices=2 UUID=..
    spares=1
ARRAY /dev/md1 level=raid1 num-devices=2 UUID=..
    spares=1
ARRAY /dev/md2 level=raid1 num-devices=2 UUID=..
    spares=1
ARRAY /dev/md3 level=raid1 num-devices=2 UUID=..
    spares=1
ARRAY /dev/md4 level=raid1 num-devices=2 UUID=..
    spares=1
ARRAY /dev/md5 level=raid1 num-devices=2 UUID=..
    spares=1
ARRAY /dev/md6 level=raid1 num-devices=2 UUID=..
    spares=1
ARRAY /dev/md7 level=raid1 num-devices=2 UUID=..
    spares=1


mount:
/dev/md1 on / type ext4 (rw,errors=remount-ro)
/dev/md2 on /tmp type ext4 (rw)
/dev/md0 on /boot type ext3 (rw)
/dev/md3 on /var type ext4 (rw)
/dev/md5 on /home type ext4 (rw,user_xattr)
/dev/md6 on /data
/dev/md7 as swap

Did I miss some important step? (I thought that my setup was prepared 
for a hard drive failure)

I appreciate your help!
Franz