There are two main ways to upgrade from ESXi 3.5 to ESXi 4.0. Both methods perform an in-place upgrade of ESXi, which allows the following:

  • preserve VMFS and all contents on local disk, if upgrading ESXi Installable
  • upgrade ESXi embedded, whether on internal or external USB key or internal flash memory
  • preserve almost all configuration data, including your networking, security, and storage configuration. The only configuration not preserved is related to licensing, because a new ESXi 4.0 license is required after the upgrade.

If you are using vCenter to manage your host, the best way to upgrade is to use vCenter Update Manager. You need to update your vCenter to vCenter 4.0 first, but that can be a first, separate step since vCenter 4.0 can manage both ESXi 3.5 and ESXi 4.0 systems. vCenter 4.0 Update Manager has been enhanced to specifically perform the upgrade process for both ESXi as well as ESX. VMwareTips has a nice video showing the entire upgrade process with Update Manager.

If you are not using vCenter, then you can use the standalone Host Update Utility to perform an upgrade. This tools installs on any Windows host, and can be used to upgrade any number of ESXi hosts. VM Help (the home of the unofficial ESXi Whitebox HCL) has a nice overview with screenshots of using Host Update Utility to upgrade ESXi 3.5 to ESXi 4.0.

More detail on the upgrade process from ESXi 3.5 to ESXi 4.0 may be found in the vSphere Upgrade Guide

About the Author

Charu Chaubal is the Director of Technical Marketing for the Cloud Platform Business Unit at VMware, and runs the team that works on the vSphere product line. He has been at the company since 2006, and has been responsible for customer education and sales enablement for a wide range of datacenter technologies, such as hypervisor security, hyperconverged storage, and virtualization of data science applications. Previously, he worked at Sun Microsystems, where he had over 7 years experience with architecting distributed resource management and HPC infrastructure software solutions.