Re: QCOW2 to RBD format 2 in one step

[Leen Besselink <leen@consolejunkie.net>]

On Tue, May 14, 2013 at 12:16:32PM +0200, Wido den Hollander wrote:
> Hi,
> 

Hi Wido,

> While working on the CloudStack code for 4.2 I'm running into some
> problems with QCOW2 and RBD format 2.
> 
> A quick cap of the problem:
> 
> CloudStack stores all the templates on "Secondary Storage" as QCOW2 files.
> 
> When a VM is deployed, this image will be copied (once) from
> Secondary Storage to Primary Storage, this is done by qemu-img which
> does the conversion.
> 
> When the image is on Primary Storage it will be copied to the
> destination volume and the Instance/VM is started.
> 
> In that last step I want to use layering, but the problem is that my
> image is RBD format 1 due to the qemu-img copy.
> 
> I can skip the qemu-img copy, but I have to find a way to go from
> QCOW2 to RBD format 2 in preferably one step. There is a issue about
> this in the tracker [0], but that won't be finished on time.
> 
> Another idea would be to do QCOW2 -> RAW -> RBD format 2, but that
> extra step will take a lot of time. It would also require some
> temporary storage on the hypervisor.
> 
> I also thought of creating the RBD image prior to converting to it,
> but that fails, since qemu-img won't let you convert to a already
> existing image.
> 
> Any brights ideas? Maybe even doing the QCOW2 -> RAW format in
> memory? In Java?
> 

I'm no expert, but would it be possible to change qemu-img to support writing RAW to standard out ?

So you can run qemu-img convert and pipe that drectly to the rbd import command ?

rbd import already supports standard in I believe.

Then you don't need any temporary storage.

Maybe something more efficient than RAW is possible as well ?

> The goal is to go from QCOW2 to RBD format 2 in one step.
> 
> [0]: http://tracker.ceph.com/issues/4897
> 
> -- 
> Wido den Hollander
> 42on B.V.
> 
> Phone: +31 (0)20 700 9902
> Skype: contact42on
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