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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