← Back to team overview

openstack team mailing list archive

Re: Should we discourage KVM block-based live migration?

 

Waiting Daniel's reply, but afaik, the new NBD server is available since qemu-1.4 and libvirt 1.0.2
Daniel, feel free to confirm or blame me.

Btw, kvm capabilities are available in upstream qemu since qemu-1.3 which works like a charm with Nova (Folsom).
-Sylvain

Le 24/04/2013 23:23, Lorin Hochstein a écrit :


On Wed, Apr 24, 2013 at 11:59 AM, Daniel P. Berrange <dan@xxxxxxxxxxxx <mailto:dan@xxxxxxxxxxxx>> wrote:

    On Wed, Apr 24, 2013 at 11:48:35AM -0400, Lorin Hochstein wrote:
    > In the docs, we describe how to configure KVM block-based live
    migration,
    > and it has the advantage of avoiding the need for shared storage of
    > instances.
    >
    > However, there's this email from Daniel Berrangé from back in
    Aug 2012:
    > http://osdir.com/ml/openstack-cloud-computing/2012-08/msg00293.html
    >
    > "Block migration is a part of the KVM that none of the upstream
    developers
    > really like, is not entirely reliable, and most distros
    typically do not
    > want to support it due to its poor design (eg not supported in
    RHEL).
    >
    > It is quite likely that it will be removed in favour of an
    alternative
    > implementation. What that alternative impl will be, and when I will
    > arrive, I can't say right now."
    >
    > Based on this info, the OpenStack Ops guide currently recommends
    against
    > using block-based live migration, but the Compute Admin guide has no
    > warnings about this.
    >
    > I wanted to sanity-check against the mailing list to verify that
    this was
    > still the case. What's the state of block-based live migration
    with KVM?
    > Should we say be dissuading people from using it, or is it
    reasonable for
    > people to use it?

    What I wrote above about the existing impl is still accurate. The new
    block migration code is now merged into libvirt and makes use of an
    NBD server built-in to the QMEU process todo block migration. API
    wise it should actually work in the same way as the existing
    deprecated
    block migration code.  So if you have new enough libvirt and new
    enough
    KVM, it probably ought to 'just work' with openstack without needing
    any code changes in nova. I have not actually tested this myself
    though.

    So we can probably update the docs - but we'd want to checkout just
    what precise versions of libvirt + qemu are needed, and have someone
    check that it does in fact work.


Thanks, Daniel. I can update the docs accordingly. How can I find out what are the minimum versions of libvirt and qemu are needed?

Also, I noticed you said "qemu" and not "kvm", and I see that http://wiki.qemu.org/KVM says that qemu-kvm fork for x86 is "deprecated, use upstream QEMU now". Is it the case now that when using KVM as the hypervisor for a host, an admin will just install a "qemu" package instead of a "qemu-kvm" package to get the userspace stuff?

Lorin




_______________________________________________
Mailing list: https://launchpad.net/~openstack
Post to     : openstack@xxxxxxxxxxxxxxxxxxx
Unsubscribe : https://launchpad.net/~openstack
More help   : https://help.launchpad.net/ListHelp


References