Re: software mirroring of boot drive (Grunloh, Robert)

[Joshua Baker-LePain <jlb17 duke edu>]

On Fri, 25 Jun 2004 at 1:13pm, taroon-list-request redhat com wrote

> you all were so good at answering my last beginner question, I have another.
> I'm trying to set up a rhel 3 server with 2 18gig scsi drives, where each
> disk has the entire os and mirrors the other, so that we have no downtime if
> either drive fails. The machine doesn't have hardware raid, so I've
> partitioned it as sda1 & sdb1 /boot and sda2 & sdb2 /  and then created md0
> and md1 during the install (raid 1). From what I can tell everything is
> working once booted.
> 
> However if, as a test, I tell the scsi card's bios to boot off of the 2nd
> drive it just hangs (no errors) before the grub menu appears. Same behavior
> if I unplug the first drive. If I unplug the 2nd drive it boots ok but
> complains about degraded mode, as expected.
> 
> I suspect the partitions are mirrored but grub isn't properly installed on
> the second drive's MBR or isn't aware of it. However I can't seem to
> unmirror them to work on the problem, since they're in use, not that I'm
> good with grub anyway. -- I must be missing something obvious.

Unfortunately, GRUB doesn't understand software RAID.  As someone else 
said, I *believe* that manually installing GRUB onto the MBR of sdb would 
work.  Test.

It's a shame that RHEL doesn't include LILO.  LILO *does* understand md, 
and will automatically install itself on every hard drive necessary if you 
tell it 'boot=/dev/md0'.  I have a couple servers running RH7.3/9 that 
boot this way, and it's always just worked.

Good luck.

-- 
Joshua Baker-LePain
Department of Biomedical Engineering
Duke University