[one-users] Disks device mapping wrong in docs ?

[Olivier Berger]

Hi.

On Mon, 21 May 2012 15:16:38 +0200, Olivier Berger <olivier.berger at it-sudparis.eu> wrote:
> Hi.
> 
> I've read
> http://opennebula.org/documentation:rel3.4:template#disks_device_mapping
> which states that :
> 
>   OpenNebula will mount the disks as follows:
> 
>     sda: OS type Image.
>     sdb: Contextualization CDROM.
>     sdc: CDROM type Image.
>     sdd: Swap disk.
>     sd[e,f,g…]: DATABLOCK type Images.
> 
> However, from what I can see (under 3.2, but the docs are the same), I
> have
> 
> sda : boot disk ln-ed from my persistent image
> sdb : swap
> sr0 : contextualization CD
> 
> Is this mapping dependant of the virtulizer (I'm using KVM).
> 
> Is the docs wrong, or is this an hypothetical example ?
> 

Furthermore, I've tested ab it more on my Debian testing system with
3.2.1, and it seems that adding a new DISK with TYPE fs with TARGET =
sdc will actually result in Debian booted in the VM mapping it to sda
:-/

Hopefully, the disks in the Debian image use UUID and not fixed path,
but that's a bit confusing.

Maybe the order of the disks detection by Linux inside the VM isn't
predictable, and there's a very good use case for UUIDs here, but,
then... is the sda,sdb... numbering style values for TARGET really
accurate ?

AFAICT from the kvm generated command line generated from the template,
they're mapped to numbered ide disks... maybe that's in fact just a
numbering depending on the order of appearance in the template file ?

Maybe using ide0,ide1,ide2 and not sda,sdb,sdc would not convey some
kind of idea that the mapping would be respected inside the running VM ?

I must admit I haven't dug any further in the libvirt definition file
generated, and the likes, so there's maybe other parameters I've
overlooked...

Does this make sense ?

Should there be a warning in the "Disks Device Mapping" section of the
Virtual Machine Definition File docs that the order detected in the
running Linux VMs can't be guaranteed ?

Thanks in advance.

Best regards,
-- 
Olivier BERGER 
http://www-public.it-sudparis.eu/~berger_o/ - OpenPGP-Id: 2048R/5819D7E8
Ingenieur Recherche - Dept INF
Institut Mines-Telecom, Telecom SudParis, Evry (France)