[WBEL-users] Software raid and User Mode Linux CD burning on WBEL

[Alex Tkachenko]

On Tue, 2004-08-03 at 18:13, Joe Pruett wrote:
> On Tue, 3 Aug 2004, Alex Tkachenko wrote:
> 
> > > Huh? Grub groks mirrors if you tell it to.  I've got my boot disk on
> > > a mirror.  If it crashes, can be sorta painful that I have to go
> > > fiddle with the BIOS to ignore the first drive.
> > How did you manage to make grub to update the second drive's boot
> > sector? AFAIK, it does not do this automatically, you have to take extra
> > steps to make it happen. Lilo did that.
> > 
> > Needless to say, you need to update your second drive's MBR *before*
> > your first one dies - I actually got caught by this problem :)
> 
> grub>device (hd0) /dev/hdc
> grub>root (hd0,0)
> grub>setup (hd0)
> 
This is exactly what I meant by 'extra steps'. I haven't seen it
mentioned anywhere (and got used to the default lilo behavior) and all
of a sudden my primary hd went down (I was trying BIOS upgrades). It
came back again, but the damn raid replication process restored the
(wrong) mbr from the mirror (or at least this is how I could explain
what happened) and I had to use the recovery CD. BTW, how that is
possible - I thought the MBR is not part of any partition, is it? I
actually have three raid'ed partitions - boot, swap and lvm, with boot
being the first - sfdisk shows it starts at 0+ - does it mean this
includes the MBR?

So I would highly recommend to anybody using software raid with grub
update the boot sector on the slave drive right after the first install.

Have a great day,
Alex

> that puts a grub boot block onto hdc telling grub to treat that disk as 
> hd0.  you only need to do this once, not every time you update grub.conf.
> 
> google for: software raid grub how-to
> 
> and you should come up with more info.
> 
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