[libvirt-users] Live Block Migration with additional attached storage

[Chun-Hung Chen]

Hi Eric,

As QEMU 1.2 is released, I don't find the feature you describe in the
change log. http://wiki.qemu.org/ChangeLog/1.2
Does it mean that we will not have this feature in the coming release?
Thanks.

Regards,
Chun-Hung

On Wed, Jul 11, 2012 at 7:37 AM, Eric Blake <eblake at redhat.com> wrote:

> On 07/10/2012 04:24 AM, Chun-Hung Chen wrote:
> > Dear all,
> >
> > I am planning to use live block migration with one VM running on local
> disk
> > and also attached additional disk from iSCSI or other shared storage.
> > When block migration, not only local VM disk is copied to the destination
> > but also the attached additional disk from shared storage. It is not
> > desired in this situation.
> > I just want the local VM disk is copied. Is there anyway to do this
> > scenario?
>
> Unfortunately, block migration during migration is an all-or-none
> prospect.  And qemu 1.1 does not provide enough tools to do anything
> differently, short of creating a snapshot file where the snapshot delta
> is on shared storage, and then you manually copy the backing file into
> place on the destination, then migrate without copying storage; but
> there is no way to coalesce things back into one file once you take the
> snapshot.
>
> Qemu 1.2 will be adding some new features that allow for block storage
> migration as well as live commits (coalescing a delta snapshot file back
> into its backing file) which can then be exposed through libvirt to
> provide more functionality into what you want to do.
>
> > Does the concept of storage pool help this? I browse the source
> > code but don't find hints right now.
>
> A storage pool lets you inform libvirt where your shared storage lives,
> but does not help with the aspect of whether live storage migration is
> possible in the underlying qemu.
>
> --
> Eric Blake   eblake at redhat.com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>
>
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