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


From: Yaodong Yang
Subject: Re: [Qemu-devel] vm live storage migration approach.
Date: Fri, 30 Jan 2015 14:13:50 -0600

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 <address@hidden> 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
address@hidden or address@hidden
Computer Science and Engineering Department
University of Nebraska-Lincoln
Lincoln, NE, USA

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