I recently upgraded a cluster of ESXi 5.1 hosts to 5.5 and learned a lesson about using a NIC that requires a third party driver.  All of my hosts are using Qlogic 10Gb CNA cards which requires a driver to be loaded (a custom vib).  Unfortunately if you try to upgrade to 5.5 using Update manager it disables the third party drivers before actually doing the update.  Since Update manager does the update over the network interface as soon as that driver is disabled the host loses contact with vCenter and Update manager and the upgrade hangs.  Luckily nothing has actually been done yet and the host can simply be rebooted and it will come back up as though nothing has been changed.  The solution is to always do the upgrade using the ISO (either as a physical DVD or USB flash drive or network mounted via a management card like an iLO on HP servers) so that there is no networking required during the upgrade.  Once the upgrade is completed I was able to install the newer driver for ESXi 5.5 and a reboot later and my host was back in business.

So the lesson learned is be very careful if using third party drivers not part of the base ESXi image.  It always seems to be safer to interact with the host directly rather than using vCenter for upgrades (never had an issue yet with patches though) if third party drivers are involved at all.

The next time I have to upgrade I think I may try to create a custom ISO with my third party drivers already integrated just to avoid the extra steps.  If I do I’ll try to post about the process and how it went.