Open Stack

On Wed, Feb 25, 2015 at 02:08:32PM +0000, Gary Kotton wrote:
> Hi,
> There is an issue with the statistics reported when a nova compute
> driver has shared storage attached. That is, there may be more than
> one compute node reporting on the shared storage. A patch has been
> posted - https://review.openstack.org/#/c/155184. The direction here
> was to add a extra parameter to the dictionary that the driver
> returns for the resource utilization. The DB statistics calculation
> would take this into account and then do calculations accordingly.
> I am not really in favor of the approach for a number of reasons:
> 
>   1.  Over the last few cycles we have been making a move to trying
>       to better define data structures and models that we use. More
>       specifically we have been moving to object support
>   2.  A change in the DB layer may break this support.
>   3.  We are trying to have versioning of various blobs of data that
>       are passed around
> 
> My thinking is that the resource tracker should be aware that the
> compute node has shared storage and the changes done there. I do
> not think that the compute node should rely on the changes being
> done in the DB layer - that may be on a different host and even
> run a different version.

Agreed, the change proposed is really unpleasant in many ways, and
also looks to be broken wrt RBD and broken wrt disk_least_available
calculations.

> I understand that this is a high or critical bug but I think that
> we need to discuss more on it and try have a more robust model.

What I'm not seeing from the bug description is just what part of
the scheduler needs the ability to have total summed disk across
every host in the cloud. It doesn't really make much sense to me
as a value to even calculate in the first place when you're choosing
which individual host to place a guest on . At least not from
a functional POV, perhaps informative from POV of an admin wishing
to see total spare capacity in their cloud, but even that's rather
crude.

What is the actual bad functional behaviour that results from this
bug that means it is a high priority issue to fix ?

Regards,
Daniel
-- 
|: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org              -o-             http://virt-manager.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org       -o-       http://live.gnome.org/gtk-vnc :|