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Re: grub2 and Linux software RAID devices
From: |
Sam Morris |
Subject: |
Re: grub2 and Linux software RAID devices |
Date: |
Tue, 5 Feb 2008 00:44:38 +0000 (UTC) |
User-agent: |
Pan/0.132 (Waxed in Black) |
On Mon, 04 Feb 2008 23:43:38 +0100, Robert Millan wrote:
> On Mon, Feb 04, 2008 at 09:36:45PM +0000, Sam Morris wrote:
>> Hi there,
>>
>> A while ago, I tried grub2 on my Debian system, which has my root
>> filesystem on a Linux software RAID-1 array. I ran into some problems,
>> and while they were raised here, nothing really came of them. Robert
>> Millan suggested I post my problem again to see if anything can be done
>> to fix it.
>>
>> I think my problems stem from the Promise IDE controller that my second
>> disk is connected to. It does not support 48-bit LBA addressing, and so
>> any attempt to read the end of the disk using BIOS calls will fail. Of
>> course, once an operating system has loaded its own driver for the
>> controller, the disk can be read correctly.
>>
>> Here's what the two disks look like:
>>
>> Model: Maxtor 6L300R0 (ide)
>> Disk /dev/hdb: 300GB
>> Sector size (logical/physical): 512B/512B Partition Table:
>> msdos
>>
>> Number Start End Size Type File system Flags
>> 1 32.3kB 543MB 543MB primary
>> 2 543MB 300GB 300GB primary ext3 raid
>>
>> The first partition is swap, the second is the root filesystem.
>>
>> The first problem is the operation of the grub-probe partition.
>> Debian's post-install script runs the following command to determine
>> which modules to include in the generated core.img file:
>>
>> grub-probe --target=partmap --device-map=/boot/grub/device.map
>> /boot/grub
>>
>> Which fails with the error:
>>
>> grub-probe: error: Cannot detect partition map for md0
>>
>> It appears that grub-probe expects to find a partition table inside the
>> RAID device, when of course, it is really in its containing device,
>> /dev/hdb.
>
> This is a known problem, and I roughly have a solution in mind, but I
> haven't been able to reproduce it. When I try to install Debian with
> /boot inside an LVM, the installer hangs. This option doesn't seem to
> be supported at all.
Ouch... I have never tried /boot on LVM myself (since grub legacy can't
handle it). However /boot on RAID works fine, I suggest you try that
instead.
>
> Furthermore, how do you boot that system with GRUB Legacy?
As far as grub1 is concerned, /dev/hdb2 is a normal partition containing
an ext3 filesystem.
> If you give me some details on how to reproduce the scheme in which
> /boot is behind a lvm/raid abstraction, I could try to get this fixed.
It's pretty simple, assuming you are using d-i. When partitioning,
configure two disks with identical partition layouts (a single partition
on each is sufficient). Then, tell partman that you want to use them as
'physical volumes for RAID'. A new option should appear, 'configure
RAID' (or something similar). Here you can create a RAID1 array using
both the partitions, which you can use as an ext3 filesystem, mounted
at /.
>> Debian's post-install script has actually been written to substitute
>> 'pc gpt' if the partmap probing fails,
>
> Actually, this was reverted a while ago.
>
>> manually. However, I now hit the second problem: the menu that grub
>> presents has no text! It seems to have an entry, however, as there is a
>> highlighted line.
>
> Which version did you try? Is it more recent than 1.96 ? We fixed bugs
> producing this result recently.
Damn, I installed the version from testing by mistake. I will try again
with version 1.96+20080203-1.
>> Jeroen Dekkers previously suggested a patch to suppress the 'out of
>> disk' error, at
>> <http://www.mail-archive.com/address@hidden/msg02873.html> but no
>> one ever committed it.
>
> Ah, I see. The patch looks correct to me; only the description you
> gave before isn't.
Hmm, I don't understand the difference between your changelog entry and
my description, but ok. :)
--
Sam Morris
http://robots.org.uk/
PGP key id 1024D/5EA01078
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Re: grub2 and Linux software RAID devices, Robert Millan, 2008/02/07