Open Stack

Hi!

I think it's a pretty useful feature, a good compromise. As you said using
a shared fs implies a lot of things and can dramatically decrease your
performance rather than using the local fs. I tested it and I will use it
for my deployment. I'll be happy to discuss more deeply with you about this
feature :)

I also feel a little concern about this statement:

 It don't work so well, it complicates migration code, and we are building
> a replacement that works.


I have to go further with my tests, maybe we could share some ideas, use
case etc...

Cheers!

On Mon, Aug 6, 2012 at 3:08 PM, Blair Bethwaite <blair.bethwaite at gmail.com>
wrote:
> Hi all,
>
> KVM block migration support in OpenStack
> (https://blueprints.launchpad.net/nova/+spec/kvm-block-migration)
> seems to be somewhat of a secret - there's almost nothing in the
> docs/guides (which to the contrary state that live migration is only
> possible with shared storage) and only a couple of mentions on list,
> yet it's been around since Diablo. Should this be taken to mean it's
> considered unstable, or just that no-one interested in documenting it
> understands the significance of such a feature to deployment
> architects? After all, decent shared storage is an expensive prospect
> with a pile of associated design and management overhead!
>
> I'd be happy to contribute some documentation patches (starting with
> the admin guide) that cover this. But first I'd like to get some
> confirmation that it's here to stay, which will be significant for our
> own large deployment. We've tested with Essex on Ubuntu Precise and
> seen a bit of weird file-system behaviour, which we currently suspect
> might be a consequence of using ext3 in the guest. But also, there
> seems to be some associated lag with interactive services (e.g. active
> VNC session) in the guest, not yet sure how this compares to the
> non-block live migration case.
>
> We'd really appreciate anybody actively using this feature to speak up
> and comment on their mileage, especially with respect to ops.
>
> I'm slightly concerned that KVM may drop this going forward
> (http://www.spinics.net/lists/kvm/msg72228.html), though that would be
> unlikely to affect anybody deploying on Precise.
>
> --
> Cheers,
> ~Blairo
>
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