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On 11/13/2019 8:34 AM, Sylvain Bauza wrote:
>> Me too. To be clear, I don't think operators would modify the above but
>> if so, they would need reshapes.

> Maybe not, but this is the kind of detail that should be in the spec and
> functional tests to make sure it's solid since this is a big
> architectural change in nova.

It depends on how the aggregates are created on the nova and placement side.

A) From placement point of view, operator can create a new aggregate and add shared storage RP to it (tag MISC_SHARES_VIA_AGGREGATE trait to this RP). The newly created valid UUID would then be set in the config option ``sharing_disk_aggregate`` on the compute node side. This aggregate UUID wouldn't be present in the nova aggregate. so it's not possible to add host to the nova aggregate unless a new aggregate is created on nova side.

B) If nova aggregates are synced to the placement service and say below is the picture:

Nova:

Agg1 - metadata (pinned=True)
 - host1
 - host2

Now, operator adds a new shared storage RP to Agg1 on placement side and then set Agg1 UUID in ``sharing_disk_aggregate`` on compute nodes along with ``using_shared_disk_provider`=True``, then it would add compute node RP to the Agg1 on the placement without any issues but when you want to reverse the configuration, using_shared_disk_provider=False, then it not that straight to remove the host from the placement/nova aggregate because there would be other traits set to compute RPs which could cause those functions stop working.

We had same kind of discussion [1] when implementing forbidden aggregates where we want to sync traits set to the aggregates but later it was concluded that operator will do it manually.

I will include the details Matt has pointed out in this email in my next patchset.

[1] : http://lists.openstack.org/pipermail/openstack-discuss/2019-June/006950.html

Regards,
tpatil



________________________________________
From: Matt Riedemann <mriedemos at gmail.com>
Sent: Wednesday, November 13, 2019 11:41 PM
To: openstack-discuss at lists.openstack.org
Subject: Re: [nova][ptg] Allow compute nodes to use DISK_GB from shared storage RP by using aggregate relationship

On 11/13/2019 8:34 AM, Sylvain Bauza wrote:
> Me too. To be clear, I don't think operators would modify the above but
> if so, they would need reshapes.

Maybe not, but this is the kind of detail that should be in the spec and
functional tests to make sure it's solid since this is a big
architectural change in nova.

--

Thanks,

Matt

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