[et-mgmt-tools] koan --virt: lvm support

[Daniel P. Berrange]

On Tue, Sep 04, 2007 at 01:55:53PM -0400, Michael DeHaan wrote:
> Johan Huysmans wrote:
> >well... it is possible ;)
> >because we are allready doing this for over a year.
> >  
> 
> The word on the street (from Dan Berrange) is that this feature is not 
> guaranteed to work in future
> versions of Xen. 

To be a little more verbose....

Virtual machines are assigned virtual *disks*. ie hdN, sdN (for full virt) or
xvdN (for paravirt).  Names like  sda1 are partitions, and not disks. It makes
no conceptual sense to have a partition without an enclosing disk. If you want
to have a 1-1 mapping between the backing files & disks inside the guest, then
simply don't partition the disk inside the guest - format /dev/sda directly.
Xen paravirt only happens to allow you to map a file straight through as a 
partition, and while it may currently work, I can make absolutely no guarentees
it will work in the future as the Xen paravirt kernel evolves - particularly
as Xen increasingly merges into LKML trees. NB with the LKML merge the ability
to hijack hdN and sdN in paravirt guests has been removed - paravirt can only
use xvdN devices now. I've not checked if hijacking partitions as described
below works, but I would not be surprised if it doesn't. Finally its also not
portable to Xen fullyvirt, or KVM, or QEMU, etc. Basically unsupportable in
the medium-to-long term.

> >And the installation is quite simple:
> >* you create your logical volumes in the dom0 and mount them
> >* you install a minimal system with yum --installroot=
> >* you create a xen config where you map the logical volumes to the
> >partition inside the domU.
> >
> >The installation instructions can be found on my blog:
> >http://www.raskas.be/blog/howtos/centos-base-image/
> >
> >And this is how the disk section of my xen config looks like:
> >disk = ['phy:vm_volumes/root-host1,sda1,w'
> >        ,'phy:vm_volumes/swap-host1,sda2,w'
> >        ,'phy:vm_volumes/tmp-host1,sda3,w'
> >        ,'phy:vm_volumes/varlog-host1,sda6,w'
> >        ,'phy:vm_volumes/home-host1,sda7,w'
> >        ]
> >
> >It would be really great if this would be possible to do with koan,
> >for now we do this with our own create vhost script.
> >

Dan.
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