[openstack-dev] [Nova] Let's set instance.root_gb=0 for volume-backed instances

Feodor Tersin ftersin at hotmail.com
Fri Jun 26 13:42:09 UTC 2015

There are several problems in algorithms which calculate size of host local disk space consumed by a volume-backed instance [1]. Obviously the volume-backed instance does not use the host local disk for the root volume. But these algorithms use root_gb, min_size, size which are not 0 for volume-backed instance. This leads to the problems.

Some solutions have been proposed to solve these problems [2]. One problem was even discussed here [3]. However all these solutions are aimed at correcting specific algorithms to allow them to take into account a type of an instance. But this does not affect other algorithms, which also use root_gb as local space size [4]. I.e. other similar problems are retained.

I propose to fix all of this by setting 0 for root_gb, min_size, size [5], since 0 is a natural value of these attributes.
Any objections?

[1] https://bugs.launchpad.net/nova/+bug/1334974
[2] https://review.openstack.org/#/c/136284/
[3] http://lists.openstack.org/pipermail/openstack-dev/2015-March/058138.html
[4] https://github.com/openstack/nova/blob/master/nova/notifications.py#L407https://github.com/openstack/nova/blob/master/nova/scheduler/host_manager.py#L250
[5] https://bugs.launchpad.net/nova/+bug/1469179

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