Open Stack

Hi,

here migration and evacuation are getting mixed up.
In migration case you can access the ephemeral storage of your VM and thus you will copy that disk=that file (either as offline aka ‘cold’ migration or via live migration)
In evacuation case your Compute Host is either unavailable (or assumed-to-be-unavailable) and thus you can’t access (or assume that you can’t access) whatever is stored on that Compute Host
So in case your emphemeral (=root disk of VM) disk is actually on that Compute Host – then you can’t access that and thus evacuation will result in rebuild
(=taking original image from Glance and thus typically you lose whatever happened after initial booting)

But in case you have something shared underneath (like NFS) – then --on-shared-storage
nova evacuate EVACUATED_SERVER_NAME HOST_B --on-shared-storage
(I guess that it will detect that automatically even in case)
But LVM using NFS share – that sounds like something not very-straightforward (not sure if it is OK with OpenStack)

See [1] and [2]
BR,
Konstantin
[1] http://docs.openstack.org/admin-guide/compute-configuring-migrations.html#section-configuring-compute-migrations
[2] http://docs.openstack.org/admin-guide/cli-nova-evacuate.html
From: Davíð Örn Jóhannsson [mailto:davidoj at siminn.is]
Sent: Friday, September 23, 2016 2:12 PM
To: Marcin Iwinski <marcin.iwinski at gmail.com>; openstack-operators at lists.openstack.org
Subject: Re: [Openstack-operators] Evacuate host with host ephemeral storage

No I have not, I guess there is nothing else to do than just give it a go :)

Thanks for the pointer

From: Marcin Iwinski
Date: Friday 23 September 2016 at 11:39
To: David Orn Johannsson, "openstack-operators at lists.openstack.org<mailto:openstack-operators at lists.openstack.org>"
Subject: Re: [Openstack-operators] Evacuate host with host ephemeral storage



On 23 Sep 2016 at 13:25:39, Davíð Örn Jóhannsson (davidoj at siminn.is<mailto:davidoj at siminn.is>) wrote:
OpenStack Liberty
Ubuntu 14.04

I know that using block storage like Cinder you can evacuate instances from hosts, but in my case we are not yet using Cinder or other block storage solutions, we rely on local ephemeral storage, configured on using LVM

Nova.conf
[libvirt]
images_volume_group=vg_ephemeral
images_type=lvm

Is it possible to evacuate (migrate) ephemeral instances from compute hosts and if so does any one have any experience with that?


Hi Davíð

Have you actually tried the regular "nova migrate UUID" option? It does copy the entire disk to a different compute - but i'm not sure if it's working with LVM. I've also used [1] ("nova live-migrate --block-migrate UUID") in the past - but unfortunately this also wasn't LVM backed ephemeral storage.

[1] http://www.tcpcloud.eu/en/blog/2014/11/20/block-live-migration-openstack-environment/

BR
Marcin

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