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

[H C <hbc1024@xxxxxxxxx>]

Thanks for the terrific explanation.  I'm presently on 4.4 and I need
to setup some Windows VMs in the short term.  I plan to upgrade my
hardware in the medium term and will likely grab the latest Xen
version.  I can probably hold off till 4.6.


On Mon, Mar 30, 2015 at 5:15 PM, Ian Campbell <ian.campbell@xxxxxxxxxx> wrote:
> 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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