Migrating VM's

Jiri Stransky jistr at redhat.com
Wed Aug 4 08:45:14 UTC 2021

On Tue, Aug 3, 2021 at 5:04 PM Sean Mooney <smooney at redhat.com> wrote:
> On Tue, 2021-08-03 at 16:49 +0000, Jiri Stransky wrote:
> > Hello folks,
> >
> > On Thu, Jul 29, 2021 at 6:24 PM Sean Mooney <smooney at redhat.com> wrote:
> > >
> > > On Thu, 2021-07-29 at 15:28 +0000, Jiri Stransky wrote:
> > > > OS Migrate might be worth a look, it's an Ansible collection. It does
> > > > cold migration that does not require admin privileges (is runnable by
> > > > tenants who are sufficiently technically savvy).
> > > >
> > >
> > > default nova policy requrie admin right for cold migration
> > > https://github.com/openstack/nova/blob/master/nova/policies/migrate_server.py#L25-L36
> > >
> > > os-migrate is not useing nova migration apis its migrating the data and vms behind novas back.
> >
> > I used the term "cold migration" in the generic sense (migration of
> > VMs while they're stopped), not in the particular "Nova cold
> > migration" sense. While we're not using any migration-specific APIs
> > (not sure if these would work *between* clouds, incl. copying Cinder
> > volumes), we do still interact with OpenStack only through the normal
> > REST APIs, we do not touch the backing MariaDB database directly. (So
> > i do not see our approach as migrating "behind Nova's back".)
> do you run any process on the host or interact with any files on the host or libvirt/qemu in any way with
> the data migrator? if you are just using snapshots and grabign datat form glance or doing data copeis with tools in the
> vms i retract my statement but otherwise any interaction with the nova instance directly outside of the nova api would be
> out of band and behind novas back.

We do not run any process on the compute hosts. OS Migrate workload
migration must work without admin access, which also means no access
to the compute hosts.

There are tenant-owned VMs which facilitate direct data copying
between the clouds, which we call "conversion hosts", and they do one
thing on top of a pure copy: sparsification using virt-sparsify before
the copying starts. This significantly speeds up copying of "empty
space", and is only done on partitions where virt-sparsify can
recognize a filesystem that can be sparsified. (We should probably
have an option to disable this behavior, in case the user would be
interested in a pure copy including e.g. leftovers of deleted files
which are considered inaccessible empty space by the filesystem.)

Have a good day,


More information about the openstack-discuss mailing list