linux - How to boot GRUB2 so it mounts "root" on a different drive (remote server without kvm switch)

Summary:
I created a copy of the root file system on a raid array (with one disk on it), and im trying to get the system to boot off that newly copied drive.

Background:

• 2 disks of same size in server (sda, sdb)


• sdb not being used


• i am trying to transition the whole thing to a raid1 mirror


• current active partitions:
  
  
  
  
  • sda1 - boot
  
  
  • sda2 - swap
  
  
  • sda3 - root (mounted to "/")
  
  
  

I am not sure if it possible to make a full raid1 system which can boot off either drive, since I do not have kvm access (i can only tell them to help me out of a jam via troubleticket)

Done so far:

• Created partitions on sdb to match sda


• Created new raid1 array (with 1 disk)



• /dev/md3 consists of 1 disk: /dev/sdb3


• mount /dev/md3 /mnt/md3


• cp -ax / /mnt/md3


• So now I have matching copies of data on / and /dev/md3

Can I just edit GRUB2 to make /dev/md3 the root, and everything should be ok right?

I need to be absolutely sure, since I have no kvm access. I looked at /boot/grub/grub.cfg and I see this entry:

menuentry 'Ubuntu, with Linux 2.6.32-28-generic-pae' --class ubuntu --class gnu-linux --class gnu --class os {
    recordfail
    insmod ext2
    set root='(hd0,1)'
    search --no-floppy --fs-uuid --set 18de6bbd-e46d-4f89-a2c9-fa2e7fa718b7
    linux   /vmlinuz-2.6.32-28-generic-pae root=/dev/sda3 ro   
    initrd  /initrd.img-2.6.32-28-generic-pae
}

So, note the "root=/dev/sda3" part. Can I just replace that with "root=/dev/md3", then reboot??