[K12OSN] Re: how's this raid setup?

[Les Mikesell]

On Thu, 2005-09-01 at 23:27, Robert Arkiletian wrote:
> 
> What steps need to be taken to have /boot on RAID1 with the new Centos
> release?
> I'm pretty sure I can set both drives as ordered bootable in the mb
> bios but that also means GRUB needs to be on the second drive. Will
> Centos do this automagically if you setup /boot as RAID1? If not, how
> does one ensure rebooting if the main drive dies.

Grub doesn't even install correctly on the first drive of
a RAID1 with Centos. Fortunately it is not difficult to
do it by hand and you only have to do it once.  You
can either ctl-alt-F2 to a shell prompt at the end
of an install before the reboot or boot from the
install cd with 'linux rescue' and chroot to /mnt/sysinstall
after it mounts the drives for you.  Then:

grub
> device (hd0) /dev/sda
> root (hd0,0)
> setup (hd0)
> device (hd1) /dev/sdb
> root (hd1,0)
> setup (hd1)
> quit

If you are in rescue mode, exit twice to reboot. 

That assumes scsi disks and /boot as the first partition
of each.  Whether it works in practice or not will depend
partly on how the drives fail.  Some failure modes will
still hang the system.  If you simulate a failure by
removing the 1st drive in a scsi system, it will usually
boot from the 2nd but all the device names will shift
up so your swap or other unlabled partitions may land
in the wrong place.  IDE systems generally hang with
any dead drive.  If you remove one, the device names
don't change so you may have to swap the positions
to make things work - but it is still better than having
to restore a backup.

-- 
  Les Mikesell
   les at futuresource.com