[CentOS-virt] Xen to KVM migration

[Dennis J.]

Hi,
I'm thinking about how to go about migrating our Xen VMs to KVM. Migrating 
the configuraton should be easy using the virsh dumpxml/define commands but 
what is the best way to transfer the (logical volume based) images without 
too much downtime for the guest system?

Can rsync operate on logical volumes? If so I could potentially use "dd" to 
transfer an initial copy of the image to the destination host and then shut 
down the guest, rsync the logical volumes which shouldn't take too long as 
not much data has to be transfered thanks to the initial "dd" and then boot 
the guest on the new machine.

Is something like this possible or would you do something different?

Regards,
   Dennis
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Re: [CentOS-virt] Xen to KVM migration

[Grant McWilliams]

On Mon, Oct 12, 2009 at 5:48 AM, Dennis J.  wrote:

> Hi,
> I'm thinking about how to go about migrating our Xen VMs to KVM. Migrating
> the configuraton should be easy using the virsh dumpxml/define commands but
> what is the best way to transfer the (logical volume based) images without
> too much downtime for the guest system?
>
> Can rsync operate on logical volumes? If so I could potentially use "dd" to
> transfer an initial copy of the image to the destination host and then shut
> down the guest, rsync the logical volumes which shouldn't take too long as
> not much data has to be transfered thanks to the initial "dd" and then boot
> the guest on the new machine.
>
> Is something like this possible or would you do something different?
>
> Regards,
>   Dennis


Can't you just use the LV in place with KVM?


Grant McWilliams

Some people, when confronted with a problem, think "I know, I'll use
Windows."
Now they have two problems.
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Re: [CentOS-virt] Xen to KVM migration

[Dennis J.]

On 10/12/2009 06:17 PM, Grant McWilliams wrote:
>
> On Mon, Oct 12, 2009 at 5:48 AM, Dennis J.  > wrote:
>
> Hi,
> I'm thinking about how to go about migrating our Xen VMs to KVM.
> Migrating
> the configuraton should be easy using the virsh dumpxml/define
> commands but
> what is the best way to transfer the (logical volume based) images
> without
> too much downtime for the guest system?
>
> Can rsync operate on logical volumes? If so I could potentially use
> "dd" to
> transfer an initial copy of the image to the destination host and
> then shut
> down the guest, rsync the logical volumes which shouldn't take too
> long as
> not much data has to be transfered thanks to the initial "dd" and
> then boot
> the guest on the new machine.
>
> Is something like this possible or would you do something different?
>
> Regards,
>Dennis
>
>
> Can't you just use the LV in place with KVM?

I may be wrong about this but isn't running KVM on top of the Xen 
hypervisor a problem? Maybe this has changed but I thought in order to be 
able to use KVM you first have to disable the Xen hypervisor and boot into 
the regular Kernel.

Regards,
   Dennis
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Re: [CentOS-virt] Xen to KVM migration

[Grant McWilliams]

On Mon, Oct 12, 2009 at 10:30 AM, Dennis J.  wrote:

> On 10/12/2009 06:17 PM, Grant McWilliams wrote:
> >
> > On Mon, Oct 12, 2009 at 5:48 AM, Dennis J.  > > wrote:
> >
> > Hi,
> > I'm thinking about how to go about migrating our Xen VMs to KVM.
> > Migrating
> > the configuraton should be easy using the virsh dumpxml/define
> > commands but
> > what is the best way to transfer the (logical volume based) images
> > without
> > too much downtime for the guest system?
> >
> > Can rsync operate on logical volumes? If so I could potentially use
> > "dd" to
> > transfer an initial copy of the image to the destination host and
> > then shut
> > down the guest, rsync the logical volumes which shouldn't take too
> > long as
> > not much data has to be transfered thanks to the initial "dd" and
> > then boot
> > the guest on the new machine.
> >
> > Is something like this possible or would you do something different?
> >
> > Regards,
> >Dennis
> >
> >
> > Can't you just use the LV in place with KVM?
>
> I may be wrong about this but isn't running KVM on top of the Xen
> hypervisor a problem? Maybe this has changed but I thought in order to be
> able to use KVM you first have to disable the Xen hypervisor and boot into
> the regular Kernel.
>
> Regards,
>   Dennis
>


But once you have your XEN DomU config file converted to KVM you could in
effect just reboot the Dom0 into a standard kernel and use KVM.

Unless of course you're only moving one DomU to KVM then it wouldn't work.

Grant McWilliams
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