If you have standalone ESX 3.x/ESXi 3.5 hosts, you can use vSphere Host Update Utility to upgrade your hosts and the vSphere Client to upgrade your virtual machines.


You cannot upgrade from ESX 3.5 Update 5 to ESX 4.0. However, you can upgrade from ESX 3.5 Update 5 to ESX 4.0 Update 1 or later.

This scenario assumes that you do not have host clusters and you do not have vCenter Update Manager. In such a case, you probably do not have VirtualCenter either. If you do have VirtualCenter, the following process can apply to your environment as well.

The following list of tasks provides a high-level overview of the upgrade process.


If you have VirtualCenter, upgrade VirtualCenter 2.x to vCenter Server 4.0.


Make sure your database is compatible with vCenter Server 4.0. This release discontinues support for some database versions and adds support for other database versions. See the Compatibility Matrixes on the VMware vSphere documentation Web site.


Make sure that you have the required permissions to perform this procedure. See Database Prerequisites.


Take a full backup of the VirtualCenter 2.x database. See your database documentation.


Back up the VirtualCenter 2.x SSL certificates. See Back Up VirtualCenter 2.x.

The downtime required for this upgrade is based on the amount of data in the database. During this time, you cannot perform provisioning operations, such as cloning or creating virtual machines. The upgrade from VirtualCenter 2.5 is faster in comparison to the upgrade from VirtualCenter 2.0.x because of differences in changes to the database schema and the amount of data migration.

After the upgrade, the ESX hosts are automatically reconnected to vCenter Server 4.0.

For a detailed description of the upgrade procedure, see Preparing for the Upgrade to vCenter Server and Upgrading to vCenter Server 4.0.


Run the vCenter Agent Preupgrade Check tool.


Install the vSphere Client.

You can install the vSphere Client on the same machine with your previous version of the VI Client. You must have the previous version of the VI Client to connect to previous versions of VirtualCenter and ESX/ESXi.

During vSphere Client installation, install the vSphere Host Update Utility. By default, this utility is not installed. Install it if you plan to use this Windows machine to initiate host upgrades.

For a detailed description of the procedure, see Upgrade to the vSphere Client.


If your environment has vCenter Converter, upgrade it.


If your environment has vCenter Guided Consolidation, complete the consolidation plan and then upgrade it to the latest version.


Use vSphere Host Update Utility to upgrade ESX 3.x/ESXi 3.5 hosts to ESX 4.0/ESXi 4.0.

This procedure involves putting the host into maintenance mode before you upgrade the host. The downtime for the procedure depends on the network speed and the server boot time.

In case of upgrade failure, the process supports rollback to the previous release.

For a detailed description of the procedure, see Upgrade to ESX 4.0 or ESXi 4.0.


Use the vSphere Client to upgrade your virtual machines:


If they are not already powered on, power on the virtual machines and upgrade to the latest version of VMware Tools. This upgrade allows you to use the new features of ESX 4.0.


Power off the virtual machines and upgrade to the latest version of virtual hardware to take advantage of the new virtual hardware.

The virtual machine upgrade process has changed in this release. In earlier releases, the virtual hardware upgrade came before the VMware Tools upgrade. For this release, you must upgrade the VMware Tools before you upgrade the virtual hardware.


Upgrade your product licenses:


Either your new license keys are sent to you in email, or you get them using the license portal.


Apply the new license keys to your assets using the vSphere Client (or vCenter Server if you have it).

You must perform these tasks for each ESX/ESXi host and the virtual machines on the hosts.