RAID & HDD failure recovery

[Bruno Wolff III]

On Wed, Nov 15, 2006 at 19:15:49 -0600,
  Laurence Vanek <lvanek at charter.net> wrote:
> 
> Surprise! boot hangs, cant find partitions on hda (of course not).  
> drops me to simple shell.

That is an odd error message. The raid devices should have names like
/dev/md0 and only those names should appear in /etc/fstab. Grub refers
to drive numbers, not letters, so I am wondering what is giving you that
message.

There are a couple of things that can cause problems. If you lost the
only disk that grub was installed on (grub works with raw partitions
and doesn't know about raid) then you will need to boot from a rescue
CD to fix things up. Even if you made sure that grub was installed on
multiple disks you still have to worry about hard drive order as after
grub starts booting from the MBR of a device it finishes using a named
(by hard drive order) hard drive and if that drive doesn't have what
is expected on it (because that drive was lost or drives don't have the
number expected after one was removed) the system won't boot. Unfortunately
grub doesn't seem to have a way to say finish booting using the same drive
you started on. (In my case I only have two drives, so I can just set them
both to use drive 0 and be able to easily get things working with either
one drive or with one drive replaced.)

No matter what has happened, you should be able to fix things up by booting
from the rescue CD. You should be able to repartition the new hda and use
mdadm to add the partitions back into the appropiate mirrors.