Spam: [CentOS] MIrrored drives won't boot after installation

Wed May 11 14:02:01 UTC 2005
Aleksandar Milivojevic <amilivojevic at pbl.ca>

Jerry Geis wrote:
> On Cent OS 4 the very last screen says REBOOT. Before
> click that do CTRL-ALT_F2 and get a prompt.
> then enter the following commands.
> 
> This will allow the software raid arrays to boot.
> 
> grub
> find /boot/grub/stage1
> device (hd0) /dev/hda
> root (hd0,0)
> setup (hd0)
> 
> This is easier the setting up mdXXX commands after boot.

The above would install Grub only on first disk.  If it fails, you would 
be unable to boot since there's no boot loader on the second drive.  To 
correctly set it up, it is a bit more complicated than above.  There's 
several ways to do it, all of them equally correct.  Following your path 
above, he'd need to repeat the last three steps for second disk too. 
Assuming first disk is /dev/hda, and second disk is /dev/hdc, and 
assuming partition containing /boot is first partition on each disk 
((hd0,0) and (hd1,0) parameters):

# grub

grub> find /boot/grub/stage1
(hd0,0)
(hd1,0)

or "find /grub/stage1", depending on partitioning configuration.

grub> device (hd0) /dev/hda
grub> root (hd0,0)
grub> setup (hd0)

grub> device (hd0) /dev/hdc
grub> root (hd0,0)
grub> setup (hd0)

A bit more complicated alternative is using "install" command directly, 
and removing "root" line from grub.conf.  Grub can usually guess what 
should be root correctly.  Something along the lines (assuming /boot is 
separate partition, if not prepend "/boot" to all paths that don't have it):

install --stage2=/boot/grub/stage2 (hd0,0)/grub/stage1 (hd0) \
         (hd0,0)/grub/stage2 p (hd0,0)/grub/grub.conf

install --stage2=/boot/grub/stage2 (hd1,0)/grub/stage1 (hd1) \
         (hd1,0)/grub/stage2 p (hd1,0)/grub/grub.conf

The above commands are split into two lines for readability.  When 
typing them, remove "\" and type each of them as single line.  Don't 
forget to remove "root" line from /boot/grub/grub.conf if using second 
approach.

-- 
Aleksandar Milivojevic <amilivojevic at pbl.ca>    Pollard Banknote Limited
Systems Administrator                           1499 Buffalo Place
Tel: (204) 474-2323 ext 276                     Winnipeg, MB  R3T 1L7