[libvirt-users] Attaching storage to a virtual machine

Douglas Russell root at dpwrussell.com
Wed Oct 31 09:51:03 UTC 2012

On 30 October 2012 19:43, Eric Blake <eblake at redhat.com> wrote:

> On 10/30/2012 06:03 AM, Douglas Russell wrote:
> > I am slightly lost trying to attach some storage to a functioning virtual
> > machine. If this where a real machine, I would simply be trying to mount
> a
> > LVM volume.
> >
> > I have found a lot of documentation about adding storage pools, but I'm
> > unsure if that is actually what I should be doing. Is that just for
> storage
> > of the virtual machines themselves? Once I'd added my LVM volume group to
> > virsh I could see no way of then assigning one volume of that to be
> offered
> > as a logical volume to one particular virtual machine.
> >
> > I've also seen this:
> >
> http://docs.fedoraproject.org/en-US/Fedora/13/html/Virtualization_Guide/sect-Virtualization-Virtualized_block_devices-Adding_storage_devices_to_guests.html#proc-Virtualization-Adding_storage_devices_to_guests-Adding_physical_block_devices_to_virtualized_guests
> >
> > Looks like I could use that to assign one of the LVM volumes in my LVM
> > volume group to the VM.
> What is typically done is creating LVM volumes in the host, and then
> assigning that as a block device for the guest to use as though it were
> a raw disk.  The guest then does _another_ layer of PVM/LVM
> partitioning, if the guest is something that uses LVM in the first
> place.  If you want the guest to see an LVM partition created by the
> host as an LVM within the guest, without an additional layer, then you
> have to expose the PVM as the block device to the guest; this is not a
> typical setup, in part because it is then up to you to ensure that the
> host and guest are not modifying the same storage at the same time (or
> put another way, that the guest is not reading from any other LVM
> partitions than the one you wanted it to use).

Ok, I understand your answer and I feel I'm close to the solution, but I'm
still unclear on the storage pools part. In what you've described below,
these aren't used? I assume you've used attach-disk to add the LVM volume
to the guest as a block device? I definitely never intended to add the
logical volume to the guest and have it appear as a logical volume. I was,
as you say, trying to attach it as a block device.

Thanks for your response!

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