libvirt users - Feb 2014 - Re: Can I move the disk image of the guest while it is running?

Hello guys!

We want to move some guests' disk images to different locations (within
the same machine, locally), but we do not want to turn off the guests.
Can we do that while the guest is running, like live migration?

I did not find any related documentation or posts about it.

Let's say the guest has a disk at /ssd/image.raw
We want to move that to /hdd/image.raw

Is there any way to do that without interrupting the guest?

--
Üdvözlettel / Best regards

Horváth Gergely | gergely.horvath@inepex.com

IneTrack - Nyomkövetés egyszerűen | Inepex Kft.
Ügyfélszolgálat: support@inetrack.hu | +36 30 825 7646 | support.inetrack.hu
Web: www.inetrack.hu | nyomkovetes-blog.hu | facebook.com/inetrack

Inepex - The White Label GPS fleet-tracking platform | www.inepex.com

On 02/05/2014 08:58 AM, Gergely Horváth wrote:
> Hello guys!
> 
> We want to move some guests' disk images to different locations (within
> the same machine, locally), but we do not want to turn off the guests.
> Can we do that while the guest is running, like live migration?
Yes, live storage migration is possible; although at the moment, qemu is
lacking a way to restart the operation if it fails midstream, so libvirt
only allows the operation if you are willing to temporarily make your
guest transient.
> 
> I did not find any related documentation or posts about it.
> 
> Let's say the guest has a disk at /ssd/image.raw
> We want to move that to /hdd/image.raw
> 
> Is there any way to do that without interrupting the guest?
Not rigorously tested, but this should do it:

virsh dumpxml $dom > file
virsh undefine $dom
virsh blockcopy $dom /ssd/image.raw /hdd/image.raw \
  --wait --verbose --pivot
virsh define file

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

Thank you Eric,

On 2014-02-05 17:23, Eric Blake wrote:
> Yes, live storage migration is possible; although at the moment, qemu is
> lacking a way to restart the operation if it fails midstream, so libvirt
> only allows the operation if you are willing to temporarily make your
> guest transient.
What does this mean? Will I loose anything if - for example - there is
not enough space on the target device? Or it will still use the original
disk image?

AFAIK, a transient guest only means it will disappear after the
virtualisation session ends.
> virsh dumpxml $dom > file
> virsh undefine $dom
> virsh blockcopy $dom /ssd/image.raw /hdd/image.raw \
>   --wait --verbose --pivot
> virsh define file
I could not find anything about "pivot" or "pivoting"? What
does --pivot
do in this case?


Thank you.

--
Üdvözlettel / Best regards

Horváth Gergely | gergely.horvath@inepex.com

IneTrack - Nyomkövetés egyszerűen | Inepex Kft.
Ügyfélszolgálat: support@inetrack.hu | +36 30 825 7646 | support.inetrack.hu
Web: www.inetrack.hu | nyomkovetes-blog.hu | facebook.com/inetrack

Inepex - The White Label GPS fleet-tracking platform | www.inepex.com