Virtual Hardware/VM Compatibility upgrade issues

Hi all,

we are about to upgrade the virtual hardware (VM compatibility) on 8

00 VMs from version 7 to 9 on our vSphere 5.1 environment. I have read about issues with hidden network cards when the card is moved to a different position on the virtual PCI bus during the upgrade. I have tested the virtual hardware upgrade with several VMs but none of them showed this behaviour.

I know how to fix the problem but now I am looking for real world experiences.

1. What percentage can I expect to fail?
2. Are there any usefull tips, tools or scripts to ease the process of finding and fixing failed VMs?
3. What is causing a card to move a position on the virtual PCI bus (can I "predict" which VMs will have a hidden network card, e.g. a combination of a specific operating system and certain type of pci device)?

Regards,

Alfredj.