grub install/setup oddity

[Rick Stevens]

On Wed, 2005-09-28 at 11:51 -0400, Mark J Strawcutter wrote:
> Dell PE2850, RHEL4 AS installed from scratch.
> 
> /dev/sda and /dev/sdb identically partitioned
> 
> sda1 and sdb1 are md1 raid1 mounted /boot
> sda2 and sdb2 are swap
> sda3 and sdb3 are md3 raid1 mounter /
> 
> grub installed on sda as part of installation, systems booting fine.
> 
> In grub shell did:
> 
> device (hd0) /dev/sdb
> root (hd0,0)
> setup (hd0)
> 
> all worked fine without error.  But when I try to boot /dev/sdb I get thrown into
> interactive grub (ie get grub prompt).  Even more interesting is that I can, at
> this point, manually enter the root/kernel/initrd commands that are in the
> grub.conf menu entry, followed by "boot" and the system comes up.
> 
> I then went into grub shell and did the device/root/setup commands on /dev/sda
> and now it, too, throws me into interactive grub.
> 
> This says the install process "installed" grub differently than the device/root/setup
> sequence is doing - the question is, different how?
> 
> BTW - I tried running "grub-install /dev/sdb" and get:
> 
> /dev/md1 does not have any corresponding BIOS drive.

This is a BIOS weirdie.  In BIOS, the first bootable drive is given the
BIOS device value of 0x80.  The second drive is 0x81 and so on.  The
problem here is that you've set things up to boot from /dev/sdb (BIOS
drive 0x81) but the BIOS still wants to use device 0x80 (/dev/sda).

> Any suggestions what to try?  Thanks

Take a look at the "--device-map" options in grub to see how to fix the
mapping.

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- Rick Stevens, Senior Systems Engineer     rstevens at vitalstream.com -
- VitalStream, Inc.                       http://www.vitalstream.com -
-                                                                    -
-      Always remember you're unique, just like everyone else.       -
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