The intention for this upgrade was to use the VMware Host Update Utility included with the vSphere Client. However, an upgrade was in the end not possible. The reason being because the existing ESX 3.5 installation had customized partitions (specifically to fill out the local storage with /, /var, swap, etc). This was fine for ESX 3.5 but for ESX 4.0, these partitions are inside the service console VMDK stored on the local VMFS. There was only 2.5GB of space left over for VMFS on the ESX 3.5 installation.

So, the upgrade was effectively a per host rebuild to ESX 4.0. The process, however, is still simple:

• vMotion all guests off of the host to be rebuilt
• Put the host into maintenance mode
• Remove the host from the cluster
• Reboot the host and install from the ESX 4.0 media (selecting local storage to create the VMFS for the service console VMDK)
• Add the host back to the cluster

After upgrading the first host, adding it to the cluster and ensuring that it’s configuration was good, I then created a Host Profile of it and used that profile to attach to the remaining hosts and apply it’s settings to ensure full compliance. This process saved plenty of time configuring the hosts post-install. A scripted installation may have been a better option but for <5 hosts, the Host Profile utility is a very fast way to configure hosts and ensure compliance. Further, for management purposes going forward, the Host Profile utility is an excellent tool to ensure compliance of hosts.