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

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

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Thank you Stefan! Now I understand the workflow.

-Yaodong

On Fri, Jan 30, 2015 at 2:37 PM, Stefan Hajnoczi <stefanha@gmail.com> wrote:

> On Fri, Jan 30, 2015 at 8:13 PM, Yaodong Yang <yaodong.yangy@gmail.com>
> wrote:
> > 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.
>
> Hi Yaodong,
> The answers to these questions are in libvirt's source code.  It
> orchestrates live migration between two hosts.
>
> Multiple independent drive_mirror jobs can run.  That's how you handle
> multiple disks.
>
> The regular migrate command (without -b) can be used if drive_mirror
> is in place and fully synced.
>
> Libvirt sets up an NBD server on the destination host.  The source
> host runs drive_mirror to copy over the contents of the disk images.
> Once the drive_mirror command has completed syncing data the regular
> 'migrate' command can be used to send device state and RAM over to the
> destination host.
>
> See qemuMigrationDriveMirror() in libvirt.
>
> migrate -b is a legacy feature that is being replaced by drive_mirror.
>
> Stefan
>



-- 
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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