install debian on fake raid/bios raid

Gerte Hoogewerf gerte at
Fri Jul 15 23:38:20 UTC 2005

Hi Tom,

Tom McClure wrote:

>Hi there!
>Your page mentions "other distributions should follow soon"
>I would like to help with adding a debian (sarge) option.  What needs to
>be done?

Some 'small' things. The most important problem is: handling changes to
the partition table. This is just different from any other case and
simply needs attention. Normally when a partition table on a disk
changes, a program like fdisk tells the kernel to re-read the partition
table (ugh!). Re-mapping dmraid partitions can be done by re-running
dmraid, the kernel can't help us here.

The second problem is: bootloaders. For lilo a specially crafted config
file is needed. A patched lilo with device-mapper support (like the
patch that Mandriva uses by default) breaks any chance to install
dmraid. I've written a patch for lilo to make installation on
device-mapper Raids easier, but my patch on its turn breaks LVM and EVMS.
For grub it's important to load a correct device map. This can easily be
done on the the grub commandline OR by having some shell script output a
working device map to a file (and call grub to use it).

Next is: shell ({linuxrc,rc}) -scripts, configuration files and Udev.
Creating an udev rule for dmraid is tricky. Maybe we should ask Heinz to
add something like an option/argument so dmraid can be used as an udev
helper program, like devmap_name (mulipath -tools). For now there isn't
a convenient way to use Udev without having a dependancy on

So, dmraid is a little different than the conventional way of treating
"disks". Besides that, the device-mapper can provide very little info on
the BIOS point of view at the "disk", making an old-fashioned bootloader
like lilo run into errors without some help.
These problems don't make it very hard to use dmraid, but automating
things into an installer is a different story. Installers need to have
special cases for dmraid.

> -tom


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