[Openstack-operators] raw ephemeral disks and qcow2 images

Tim Bell Tim.Bell at cern.ch
Fri Oct 23 06:21:23 UTC 2015


On 22/10/15 20:01, "Marc Heckmann" <marc.heckmann at ubisoft.com> wrote:

>Hi,
>
>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
>supported.
>
>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:
>
>http://events.linuxfoundation.org/sites/events/files/slides/p0.pp_.pdf
>
>I think it would be worthwhile for Openstack (and libvirt if required)
>to support the "l2-cache-size" option for qcow2. 

+1 for l2-cache-size. This presentation was the basis under which I was looking for a temporary approach until we get the latest qcow2 support.

>
>-m
>
>>         
>>          
>>         
>>         Tim
>>         
>>          
>>         
>>         
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>
>
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