Testing the 4.3 to 4.4 migration... what I describe here is facts is mostly observations
and conjecture, could be wrong, just makes writing easier...
While 4.3 seems to maintain a default emulated machine type (pc-i440fx-rhel7.6.0 by
default), it doesn't actually allow setting it in the cluster settings: Could be
built-in, could be inherited from the default template... Most of my VMs were created with
the default on 4.3.
oVirt 4.4 presets that to pc-q35-rhel8.1.0 and that has implications:
1. Any VM imported from an export on a 4.3 farm, will get upgraded to Q35, which
unfortunately breaks things, e.g. network adapters getting renamed as the first issue I
stumbled on some Debian machines
2. If you try to compensate by lowering the cluster default from Q35 to pc-i44fx the
hosted-engine will fail, because it was either built or came as Q35 and can no longer find
critical devices: It evidently doesn't take/use the VM configuration data it had at
the last shutdown, but seems to re-generate it according to some obscure logic, which
fails here.
I've tried creating a bit of backward compatibility by creating another template based
on pc-i440fx, but at the time of the import, I cannot switch the template.
If I try to downgrade the cluster, the hosted-engine will fail to start and I can't
change the template of the hosted-engine to something Q35.
Currently this leaves me in a position where I can't separate the move of VMs from 4.3
to 4.4 and the upgrade of the virtual hardware, which is a different mess for every OS in
the mix of VMs.
Recommendations, tips anyone?
P.S. A hypervisor reconstructing the virtual hardware from anywhere but storage at every
launch, is difficult to trust IMHO.