thank you that you have taken the time leading me through the process and answering extensively.

Having digged now into the code in /nova/nova/tests/unit/virt/libvirt/test_driver.py, it is obvious that my proposal is not universal but fixes only my specific config (and make then other configs fail).

However, it seems to me that a config that

running cinder on each compute node with lvm backend
creating root volume as lvm volume
creating swap not as ephermal or swap (raw) disk but as lvm volume (as lvm/qemu does automatically)

is not a supported model in nova yet to deal with instance resizing/migrations.

Thanks again for your guidance, will go through it ...

Br Clemens