software raid and grub on FC3

[Aleksandar Milivojevic]

Ed Wilts wrote:
> It still is.  What you're asking for is a mirrored master boot record
> while mirroring partitions.  Grub has no knowledge of what software
> mirroring you may be doing or if you even have any intention of booting
> off a mirror member.

Mmmm...  No.  If you simply copy MBR from one disk to another (or 
blindly do grub-install to second disk), you'll get Grub installed on 
the second disk, but it will still be configured to read configuratin 
file from first disk.  If first disk fails, you have problem.

What you need to have (in case of Linux software RAID 1) is:

   - each copy of Grub reads stage2 and configuration from disk it is 
installed on
   - each copy of Grub loads kernel and initrd from disk it is installed on

This is something LILO does by default if you specify Linux software 
RAID 1 partition as boot disk.  Grub doesn't.

To get Grub do the right thing, you need to remove "root" command from 
grub.conf (this will make grub load kernel and initrd from corresponding 
submirror of /boot partition), and than install Grub on both disks but 
specifying partitions that hold stage1, stage2 and grub.conf files to 
point to related submirrors.

This is way more complex than configuring LILO to do the same thing, and 
is not as simple as typing "grub-install".  It isn't space science 
either, but you need to dig deep into Grub documentation (or Google 
around if you are not really into it).

> If you had a true hardware mirroring solution (RAID 5 for example),
> you'd still be done in seconds.

RAID 5 is not mirror.  RAID 5 is striping with parity.  RAID 1 is mirroring.

Anyhow, topic of this thread was "software RAID" (check the subject 
line).  Hardware RAID is something completely different.  While 
investing in hardware RAID has advantages (and it is something I warmly 
suggest), doing it just to get Grub working correctly out of the box is 
the wrong reason for making such an investment.

-- 
Aleksandar Milivojevic <amilivojevic at pbl.ca>    Pollard Banknote Limited
Systems Administrator                           1499 Buffalo Place
Tel: (204) 474-2323 ext 276                     Winnipeg, MB  R3T 1L7