[Openstack-operators] raw ephemeral disks and qcow2 images

Marc Heckmann marc.heckmann at ubisoft.com
Thu Oct 22 18:01:42 UTC 2015


On Thu, 2015-10-22 at 08:17 -0700, Abel Lopez wrote:
> I've actually looked for this for our RBD backed ephemeral instances,
> but found the options lacking. I last looked in Juno. 
> On Thursday, October 22, 2015, Tim Bell <Tim.Bell at cern.ch> wrote:
>         Has anyone had experience with setting up Nova with KVM so it
>         has raw ephemeral disks but qcow2 images for the VMs ? We’ve
>         got very large ephemeral disks and could benefit from the
>         performance of raw volumes for this.

We looked into this for the very same reasons and it doesn't seem to be

That being said, I'm fearful of the boot time performance impact of
using RAW for ephemeral. 

I suggest you check out the following presentation about qcow2
performance if you haven't already done so:


I think it would be worthwhile for Openstack (and libvirt if required)
to support the "l2-cache-size" option for qcow2. 


>         Tim
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