Linux Software Raid 1 Recovery Question

[Kent Borg]

On Wed, Sep 25, 2002 at 11:24:08AM -0400, ron.peterson at yellowbank.com wrote:
> Are you running lilo or grub?  

lilo, there is a distinct shortage of information on how to use grub
for a bootable software raid, but the two config files are similar
enough that I plan to guess at how grub would be set up and try that.

> Likely you only had an MBR written to /dev/hda.

Yes.  Getting lilo to put one on /dev/hdc and getting the bios to look
at it didn't work.  (But when all else fails, the bios also tries to
do a net boot when, as far as I can see, I have not told it to do a
lan boot.  There might be a bug in how the bios was integrated with
this board, or maybe operator error.)

> You should be able to recover by booting from, say, a RH
> installation CD in rescue mode.

I put the /dev/hdc disk back and it booted, I did some raidhotadd's
and the array has rebuilt itself.

> Try the opposite - pull /dev/hdc instead of /dev/hda.

I think I effectively did that when I did a test Mandrake installation
on /dev/hdc.  I expected that I would then be able to boot from either
disk, depending upon how I set the bios, but I still got only the
Mandrake boot screen.  I ended up using the Knoppix CD to rescue
things.  (*Very* nice to have a rescue CD that can surf the web, not
to mention play music, run Open Office, etc.!)

A co-worker did a similar experiment on his raid 1 box but he blew
away /dev/hda (to try Debian), and though we can get to everything on
his /dev/hdc via the Knoppix CD, we haven't managed to get /dev/hdc to
boot.

The lilo on the Knoppix CD is newer than RH 7.3's, and we used a new
option it has to try to install an MBR on /dev/hdc, but we still
couldn't get it to boot.

As I said, I plan to try grub next.


-kb, the Kent who figures this should be easier.