Open Stack

On Sep 18, 2013, at 4:50 PM, Josh Durgin <josh.durgin at inktank.com> wrote:

> On 09/18/2013 07:14 AM, Thierry Carrez wrote:
>> Mike Perez wrote:
>>> Currently in Havana development, RBD as ephemeral storage has serious
>>> stability
>>> and performance issues that makes the Ceph cluster a bottleneck for using an
>>> image as a source.
>>> [...]
>> 
>> This comes up a bit late, and the current RC bugs curves[1] really do
>> not encourage me to add more distraction for core reviewers.
>> 
>> The only way I could be fine with this would be for the performance
>> issue to actually be considered a bug (being so slow you can't really
>> use it without the fix), *and* the review being very advanced and
>> consensual that the distraction is minimal.
>> 
>> Could you quantify the performance issue, and address Zhi Yan Liu's
>> comments ?
> 
> In terms of performance, consider an image that's already cached on
> the hypervisor host. Using the libvirt_images_type=rbd, the locally
> cached copy is imported via the 'rbd import' command. This is a very
> slow operation, which ended up taking upwards of 15 minutes in my
> tests.
> 
> Using libvirt_images_type=qcow2, this takes roughly 0.2 seconds.
> 
> If the image was not already cached locally, it would have to be
> downloaded from glance, which would take the same amount of time
> regardless of libvirt_images_type or glance backend.
> 
> The proposed patch avoids downloading from glance and uploading to
> rbd, and results in similar times to qcow2 without requiring the image
> to be cached locally.
> 
> Josh

Its too bad that the timing is so bad because this seems like a really useful feature. It might be worth it merge a patch into icehouse ASAP and see if you can get the distros on board with backporting the patch.

Vish