Live Migration does not work unless cache=none

[Jesse Pretorius]

If O_DIRECT is not supported, 'cache=none' is not set. Thus, Live Migration gives the following error:

"Live Migration failure: Unsafe migration: Migration may lead to data corruption if disks use cache != none"

However, it is ok to migrate if the storage is "coherent" across nodes. So Nova's live-migration should support the Libvirt's unsafe=True flag.

Ideally there should be a nova flag which can be set to pass through the libvirt 'unsafe=true' flag. My thinking is that if 'cache=writethrough' is set then the underlying storage should be safe, but perhaps it's best not to make that assumption and rather to have a nova.conf flag.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/49329

[Yassine (yassine-lamgarchal)]

I noticed the options 'live_migration_flag' and 'block_migration_flag' in nova.conf which can be used for adding the flags VIR_MIGRATE_UNSAFE so that it fixes the issue.

What do you think about ?

[Jesse Pretorius (jesse-pretorius)]

Fair point. As long as the options are shown in the documentation at
http://docs.openstack.org/grizzly/openstack-compute/admin/content/configuring-migrations.html#true-live-migration-kvm-libvirt
 and
http://docs.openstack.org/grizzly/openstack-compute/admin/content/hypervisor-configuration-basics.html
then
a deployer will know that the options are available.

On 14 October 2013 18:10, Yassine <email address hidden> wrote:

> I noticed the options 'live_migration_flag' and 'block_migration_flag'
> in nova.conf which can be used for adding the flags VIR_MIGRATE_UNSAFE
> so that it fixes the issue.
>
> What do you think about ?
>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1222682
>
> Title:
> Live Migration does not work unless cache=none
>
> Status in OpenStack Compute (Nova):
> In Progress
>
> Bug description:
> If O_DIRECT is not supported, 'cache=none' is not set. Thus, Live
> Migration gives the following error:
>
> "Live Migration failure: Unsafe migration: Migration may lead to data
> corruption if disks use cache != none"
>
> However, it is ok to migrate if the storage is "coherent" across
> nodes. So Nova's live-migration should support the Libvirt's
> unsafe=True flag.
>
> Ideally there should be a nova flag which can be set to pass through
> the libvirt 'unsafe=true' flag. My thinking is that if
> 'cache=writethrough' is set then the underlying storage should be
> safe, but perhaps it's best not to make that assumption and rather to
> have a nova.conf flag.
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/nova/+bug/1222682/+subscriptions
>

--
Jesse Pretorius
mobile: [phone]
email: <email address hidden>
skype: jesse.pretorius

[Anne Gentle (annegentle)]

The code itself is abandoned. The referring URLs are grizzly. Marking as won't fix.