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Re: Disk mapping confusion with the device command

From: Phillip Susi
Subject: Re: Disk mapping confusion with the device command
Date: Thu, 10 Nov 2005 21:41:06 -0500
User-agent: Mozilla Thunderbird 1.0.7 (X11/20051010)

I got it figured out. Someone sugested those two commands but it looks like grub only wants you to tell it about the disk device, not the partition as well. It seems that it accepts device(hd0,4) only it ignores the ,4 part. I left out that line and then had to use the geometry command to specify the correct geometry for the drive and now it's working. I'm now using grub to dual boot windows and ubuntu on a sata hardware fakeraid raid 0. If anyone is interested in how, instructions can be found here:


Phillip Susi wrote:

I have an unusual disk setup where the hard disk can not be accessed using the conventional /dev/hda device. I have been trying to explain the proper mapping to grub, but it looks like it doesn't understand.

I tried to explain the mapping with these commands:

device (hd0,4) /dev/mapper/via_hfciifae5
device (hd0) /dev/mapper/via_hfciifae

As you can probably guess, the raw disk itself is accessed using the block device /dev/mapper/via_hfciifae and the first extended partition is accessed via /dev/mapper/via_hfciifae5. This partition is formatted with ext2 and I mount under /boot. The bios sees /dev/mapper/via_hfciifae as bios block device 0x80, so grub should have no trouble booting from it.

When I issue the root (hd0,4) command I get an error message stating that the partition table is corrupt. When I enable debug messages and verbose mode, I see a debug message saying that it is reading from /dev/mapper/via_hfciifae5. It looks like grub is looking for the MBR on the partition block device instead of the disk block device, and I think that is a bug.

Because I explained to grub with the device (hd0) command that it should open /dev/mapper/via_hfciifae, it should look there for the MBR, but it isn't. Am I doing something wrong or is this a bug?

For reference I am running ubuntu breezy which appears to have the package "grub (0.95+cvs20040624-17ubuntu7)" installed.

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