Re: RAID 1 and grub

Bill Davidsen wrote:

Richard Scobie wrote:

quoted

A followup for the archives:

I found this document very useful:

http://lists.us.dell.com/pipermail/linux-poweredge/2003-July/008898.html

After modifying my grub.conf to refer to (hd0,0), reinstalling grub on 
hdc with:

grub> device (hd0) /dev/hdc

grub> root (hd0,0)

grub> (hd0)

and rebooting with the bios set to boot off hdc, everything burst back 
into life.

I shall now be checking all my Fedora/Centos RAID1 installs for grub 
installed on both drives.

Have you actually tested this by removing the first hd and booting? 
Depending on the BIOS I believe that the fallback drive will be called 
hdc by the BIOS but will be hdd in the system. That was with RHEL3, but 
worth testing.

The line:

grub> device (hd0) /dev/hdc

simply means "treat /dev/hdc as the first _bios_ hard disk in the system". 
This way when grub writes to the MBR of hd0, it will be in fact writing to 
/dev/hdc. The reason the drive must be referenced as hd0 (and not hd2) is 
because grub enuerates drives according to the bios, and therefore the drive 
from which the bios is currently booting is _always_ hd0.