[PVE-User] Live VM migration 6.3 to 6.2 fails

[alexandre derumier]

On 02/12/2020 09:11, Christian Balzer wrote:
> Hello,
>
> yes I know that migrating back to an older version is not guaranteed but
> I'm rather confused as to why this happens.
>
> Firstly this, more details below:
> ---
> 2020-12-02 16:34:08 start migrate command to tcp:10.0.0.11:60000
> 2020-12-02 16:34:09 migration status error: failed
> 2020-12-02 16:34:09 ERROR: online migrate failure - aborting
> 2020-12-02 16:34:09 aborting phase 2 - cleanup resources
> 2020-12-02 16:34:09 migrate_cancel
> 2020-12-02 16:34:11 ERROR: migration finished with problems (duration 00:00:08)
> TASK ERROR: migration problems
> ---
>
> That's all I get, where would one find the exact issue?
>
> Now for the details, in the previous minor upgrade we saw a similar issue,
> but that only affected VMs which had been created on an upgraded node, old
> ones were fine to move in both ways.
> OK, that was because of new features int he VM definition not present on
> the old version, understandable.
>
> With this one on a (more frequently updated) test cluster 6.3 to 6.2
> migrations also works, the test cluster old nodes are at
> pve-manager (6.2-12), the one with issues are pve-manager (6.2-6).
> I however see nothing in the changelogs which would explain this difference.
>
> In general being able to live migrate back to a node with the previous
> version is a very desirable situation, since if there are issues/bugs (on
> the VM level) with the new version there no longer is an impact free way
> of reverting if this functionality is not present.
>
> Regards,
>
> Christian

you can't migrate from a newer qemu version to an older qemu version,

if the vm start has been started first on the newer qemu version.


if the vm was started first on an older qemu version,

you can live migrate it to a newer qemu version

and migrate it again to older qemu version.

(until you stop/start it again on a newer qemu version).


This is because, when the vm is started, it's keeping internally the 
qemu machine version

of the current qemu process version.


The only thing to keep in mind, try to keep all yours nodes at same version.

Proxmox is a rolling release, you can have qemu upgrade between 2 releases.