10.04 desktop RAID 10 install?

Tom H tomh0665 at gmail.com
Thu Jun 24 05:21:13 UTC 2010

On Wed, Jun 23, 2010 at 10:20 PM, Goh Lip <g.lip at gmx.com> wrote:
> On 06/24/2010 09:46 AM, Alan McKay wrote:
>>> Make sure your boot is non-mdadm'd or RAID1.
>> yeah, I'd read that somewhere.
>> So I ahve it working.  I have a 512M RAID1 layed across all 4 disks
>> (though looks like mdadm only took the first 3 of them but I don't
>> care).  Then 2G swap part on each of the 4 disks.  Then the rest of
>> the 1T goes to a RAID10
>> It is running and working great.  The only thing I am having trouble
>> with is grub.   It works mind you.  But one of the articles I'd read
>> said basically when doing the RAID1 approach for /boot, to make sure
>> the boot loader is installed on all of the disks in the RAID1.  And
>> damned if I know how to do that.  Been reading man pages and checking
>> google and still nothing.
> To install grub to other disks...
> grub-install --root-directory=/media/disk_other/ /dev/sdx
> Note it will *not* create grub.cfg file to the other disk.

It's not quite as simple as that.

I had said on the list some time ago that grub1 couldn't boot from an
mdadm'd /boot and that I'd never worked anywhere that did that.
Christopher C corrected me and he was right.

Out of curiosity, I checked the RHEL documentation since this is what
we run and I found:

The problem is that you have to trick grub in order to ensure that you
can boot from a degraded raid by installing grub onto sda and sdb with
both being (hd0).

For grub1, you would run (assuming /boot is on sdX1):

# grub
grub> device (hd0) /dev/sda
grub> root (hd0,0)
grub> setup (hd0)
grub> quit


# grub
grub> device (hd0) /dev/sdb
grub> root (hd0,0)
grub> setup (hd0)
grub> quit

For grub2, the only equivalent procedure that I can think of is to
back up device.map, set (hd0) as /dev/sda in device.map, run
grub-install /dev/sda, set (hd0) as /dev/sdb in device.map, run
grub-install /dev/sdb.

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