Re: [Qemu-devel] vm live storage migration approach.

[Yaodong Yang <yaodong.yangy@gmail.com>]

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An follow up questions.

Suppose I have a running VM with two virtual disks, I would like to migrate
the vm from host A to host B. Both host A and host B have their own
isolated storage devices. Is there anyway to migrate the vm's memory, two
virtual disk images and other states together from host A to host B? Can
drive_mirror command itself finish this job? I noticed that drive_mirror
only mirror for one virtual disk and require both the source and
destination share the same storage namespace. I do not know how to migrate
the whole VM (memory, storage, network ) together from host A to host B,
given that host A and host B have NO shared storage resource.

Could you show me an example, if possible?

I know "migrate -b" works well for this purpose. But the downside is
"migrate -b" does not mirror Write Requests to both host A and host B
during migration. In this case, "migrate -b" has a higher VM downtime
during the migration.

Yaodong

On Fri, Jan 30, 2015 at 1:21 PM, Eric Blake <eblake@redhat.com> wrote:

> On 01/30/2015 09:25 AM, Yaodong Yang wrote:
> > Hi all,
> >
> > I'm investigating the current schemes for the VM live storage migration
> in
> > QEMU system. I have the following questions:
> >
> > 1. What is the functionality of drive_mirror in QEMU? Is it designed as a
> > VM live storage migration approach?
>
> Yes. drive-mirror was added precisely to support live storage migration.
>
> >
> > 2. What's the difference between drive_mirror and vMotion? I learned that
> > vMotion employs IO Mirroring mechanism to migration a running VM with all
> > the virtual disk images. Are there any other mechanisms inside QEMU serve
> > this purpose as well?
>
> vMotion is not part of qemu, so I'm not sure what it does.  Therefore, I
> cannot make a fair comparison.
>
> >
> > I'm looking for a mechanism in QEMU, which is similar to vMotion ( IO
> > Mirroring) in ESX environment.
>
> Look at drive-mirror, block-backup, quorum drives, and lots of recent
> threads on this list about adding redundant processing (such as the term
> "COLO") for how to piece together lower-level blocks into whatever drive
> mirroring scheme you can think of.
>
>
> --
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>
>


-- 
Yaodong Yang
yaodong.yangy@gmail.com or yyang@cse.unl.edu
Computer Science and Engineering Department
University of Nebraska-Lincoln
Lincoln, NE, USA

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