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

[Daniel P. Berrange]

On Wed, Sep 05, 2007 at 11:18:49AM +0200, Kris Buytaert wrote:
> On Wed, 2007-09-05 at 04:28 +0100, Daniel P. Berrange wrote:
> > 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.
> 
> 
> I think it is extremely important to continue to be able to use
> filesystems on LVM volumes in dom0 as  filesystems in domU's.  Using
> them as full disks with a partition on them would be fine.  

Yes, that is entirely possible. If you have /dev/VolGroup00/MyGuestFS
in the dom0, you can map that into the guest as /dev/xvda  and simply
mount /dev/xvda itself - there is no need to pretend it is /dev/xvda1
inside the guest.

Dan.
-- 
|=- Red Hat, Engineering, Emerging Technologies, Boston.  +1 978 392 2496 -=|
|=-           Perl modules: http://search.cpan.org/~danberr/              -=|
|=-               Projects: http://freshmeat.net/~danielpb/               -=|
|=-  GnuPG: 7D3B9505   F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505  -=|