[Openstack-operators] Evacuate host with host ephemeral storage

Marcin Iwinski marcin.iwinski at gmail.com
Fri Sep 23 14:31:05 UTC 2016

double-check if "nova migrate" option will work for you - it uses a
different mechanisms than live-migration and judging by [1] depending on
the release of OpenStack you use it might work with LVM backed ephemeral
storage. And I seccond Kostiantyn email - we seems to be mixing evacuation
with migration.

[1] https://bugs.launchpad.net/nova/+bug/1270305


On 23 Sep 2016 at 16:21:17, Davíð Örn Jóhannsson (davidoj at siminn.is) wrote:

Thank you for the clarification. My digging around has thus far only
revealed https://bugs.launchpad.net/nova/+bug/1499405 (live migration is
not implemented for LVM backed storage)

If any one has any more info on this subject it would be much appreciated.

From: "Kostiantyn.Volenbovskyi at swisscom.com"
Date: Friday 23 September 2016 at 13:59
To: David Orn Johannsson, "marcin.iwinski at gmail.com", "
openstack-operators at lists.openstack.org"
Subject: RE: [Openstack-operators] Evacuate host with host ephemeral storage


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

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]




[2] http://docs.openstack.org/admin-guide/cli-nova-evacuate.html

*From:* Davíð Örn Jóhannsson [mailto:davidoj at siminn.is <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

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"
*Subject: *Re: [Openstack-operators] Evacuate host with host ephemeral

On 23 Sep 2016 at 13:25:39, Davíð Örn Jóhannsson (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





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.



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