[openstack-dev] [nova] Shared storage support

Chris Friesen chris.friesen at windriver.com
Wed Mar 11 16:06:43 UTC 2015

On 03/02/2015 06:24 PM, Jay Pipes wrote:
> On 02/25/2015 06:41 AM, Daniel P. Berrange wrote:
>> On Wed, Feb 25, 2015 at 02:08:32PM +0000, Gary Kotton wrote:
>>> 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.
> The scheduler does not need to know this information at all.

Actually, there's a valid reason for the scheduler to know this.

If I want to schedule 5 instances, each with 10GB disk, and I have 5 compute 
nodes each reporting 30 GB of space, it really does matter to the scheduler 
whether those compute nodes are all on a single shared storage device or if 
they've all got separate storage.

The scheduler is always operating off stale data (as reported by the compute 
nodes some time ago) plus its own predictions.  If its predictions don't match 
the actual behaviour then its decisions are going to be wrong.


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