dm-raid support

[David Zeuthen]

On Wed, 2009-07-29 at 22:29 +0200, Tobias Preclik wrote:
> Hello,
> 
> I wonder if dm-raid devices are already properly supported in
> DeviceKit-disks. 

To a certain degree, yeah.

> I am asking because I had problems with hal detecting
> my dm-raid devices. See here:
> 
> http://lists.freedesktop.org/archives/hal/2009-June/013403.html

Currently DeviceKit-disks will properly detect the devices and things
will look just fine in Nautilus / GTK+ file chooser or anything else
using GVfs, see https://bugzilla.redhat.com/show_bug.cgi?id=495152 for
the bug where this (and other things) was fixed.

Still, things will look pretty non-sensical in Palimpsest, e.g. this
screenshot

 https://bugzilla.redhat.com/attachment.cgi?id=339015

but that's pretty much just because fakeraid currently is implemented in
a way that completely screws over the rest of the system - e.g. using
device-mapper in "interesting ways" and conveniently removing real
partitions for physical disks.

Now, ideally things would look like what we do for md-raid

 http://people.freedesktop.org/~david/gdu-raid5.png

and maybe with the switch from dm-raid -> md-raid this can be done. I
don't know.

Anyway, to support the whole range of multi-disk solutions on Linux we'd
need to support

 - md-raid (95% done, only the "create RAID array is missing, see
   http://people.freedesktop.org/~david/gdu-create-raid-1.png and
   http://people.freedesktop.org/~david/gdu-create-raid-2.png for
   some work in progress)

 - LVM2 (not done, am planning to work on it soon)

 - btrfs (not done, am planning to work on it soon)

 - dm-raid (not done, no plans to work on it yet)

 - multipath (not done, no plans to work on it yet)

but of course this list is not complete as device-mapper conveniently
lets you configure your system in very interesting ways that completely
doesn't map to any sane UI (LVM2 is the exception).

(Personally I never understood why one would want to use fakeraid on
Linux - it's not like it is any faster than using native software raid
and it locks you into on-disk formats and makes it harder to manipulate
the arrays outside the BIOS. I bet it probably has something to do with
people dual-booting Windows. I don't know)

Anyway, hope this helps.

    David