howto boot from the second disk in raid 1

[abdelkader belahcene <abelahcene@gmail.com>]

hi,
I installed squeeze  on 2 disks sata  using  raid 1.

the system runs fine with both disks,  it runs fine with the first disk alone,
 

but it fails to  reboot from the second disk alone.
although  i installed  grub in both disks 

when i used the second disk alone,  it is detected as slave!!!!  no master disk detected!!!,
so the system reboot without stopping!!!!

is there a possibility to declare the disk as master???

thanks for help