Re: [Xen-users] existing VMs and future Xen versions

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Mon, 2015-03-30 at 15:38 +0800, H C wrote:
> Hi,
> 
> Can VMs created in an older version of Xen work in newer versions?  I
> have 4.4 running and am planning to invest in some licensed OSes
> (activating some Windows Licenses on a vms running in 4.4) .  Will I
> be stuck on 4,4 or does Xen have upgrade paths for VMs?  How is this
> sort of thing typically planned for?

Yes, this sort of compatibility is in general supported. The Xen
hypercall guest interface (used by PV and PVHVM guests) has been
supported in a stable and backwards compatible manner since Xen 3.0.

Windows licensing goes a bit further and (AIUI) operates on a points
system based on h/w changes. So it may occasionally be necessary to
tweak to your configuration when switching to a new version to retain
previous behaviour.

For example if you had installed on Xen <=4.2, which by default used the
qemu-xen-tradition device model then when you upgraded to Xen >=4.3,
which switched to the qemu-xen device model by default, then you would
need to explicitly ask to use qemu-xen-traditional in the domain
configuration, otherwise the switch in the emulated hardware might be
enough to trigger reactivation.

This sort of thing isn't very frequent though and in most cases things
just work or the changes aren't enough trigger reactivation.

Ian.


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