Thank you that way it worked. But there is another problem. After connecting one of the old hosts, loaded with a few VMs, i tried to vMotion one of them. Because the old hardware have Intel Xeon X5355 and the new Xeon E5-2640 CPUs vCenter keeps telling me that EVC needs to be enabled in order to do so.
If I'm setting the EVC in my new cluster do vMotion VMs I don't need any downtime to deactivate EVC again, right? I But I remember the VMs do need a reboot to discover the extended instruction-set.
Does anyone know which mode is required for my CPUs?