grub2 and Linux software RAID devices

[Sam Morris <sam@robots.org.uk>]

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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.

Debian's post-install script has actually been written to substitute 'pc
gpt' if the partmap probing fails, so I should still be able to boot up
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.

The third problem is that if I press enter, or wait for the timeout to
finish, or the screen blanks, and I get the message "Booting '". The
system then freezes and I have to use the hardware reset switch to
continue (ctrl+alt+del does not work). Pressing 'e', or the up or down
keys also freeze the system, without the "Booting '" message.

I am able to get to the console by pressing 'c'. Here I can attempt to
load the raid module, however I run into a fourth problem: I get the
error, "out of disk": presumably because GRUB is trying to read past the
apparent end of the disk connected to my promise controller.

Jeroen Dekkers previously suggested a patch to suppress the 'out of
disk' error, at
<http://www.mail-archive.com/grub-devel@gnu.org/msg02873.html> but no
one ever committed it.

-- 
Sam Morris
http://robots.org.uk/

PGP key id 1024D/5EA01078
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