The process of upgrading ESX/ESXi hosts includes several changes from the upgrade process in previous releases.

When you upgrade from ESX 3.x/ESXi 3.5 to ESX 4.0/ESXi 4.0, you can use either the vSphere Host Update Utility or vCenter Update Manager.

This tool is for upgrading ESX 3.x/ESXi 3.5 standalone hosts to ESX 4.0/ESXi 4.0 and for patching ESXi 4.0 standalone hosts. A standalone host is an ESX/ESXi host that is not managed in vCenter Server.

This utility is intended for small deployments with fewer than 10  ESX/ESXi hosts and without vCenter Server or vCenter Update Manager. The utility includes a wizard that guides you through upgrades. While an upgrade is in progress, the utility provides visual status.

vCenter Update Manager is for upgrading ESX/ESXi hosts that are managed in vCenter Server.

With Update Manager 4.0 and later, you can perform orchestrated upgrades of hosts and virtual machines. Orchestrated upgrades allow you to upgrade all hosts in the inventory by using host upgrade baselines. You can use orchestrated upgrades to upgrade the virtual hardware and VMware Tools of virtual machines in the inventory at the same time, using baseline groups containing the following baselines:

VM Hardware Upgrade to Match Host

VMware Tools Upgrade to Match Host

Orchestrated upgrades can be performed at a cluster, folder or datacenter level.

This significantly simplifies the upgrade of hosts and virtual machines.

In addition, this tool enables you to configure policy-based compliance monitoring and remediation. For example, you can define a host upgrade baseline to upgrade an ESX host to ESX 4.0, a virtual machine upgrade baseline to upgrade the virtual machine hardware to the latest version, and VMware Tools to the latest version. To do this, you use wizard-based workflows to first schedule host upgrades for an entire cluster and then schedule a virtual machine upgrade for all the virtual machines.

Built-in best practices in the wizard workflows prevent erroneous upgrade sequences. For example, the wizard prevents you from upgrading virtual machine hardware before you upgrade hosts in a cluster. vCenter Update Manager monitors hosts and virtual machines for compliance against your defined upgrade baselines. Noncompliance appears in detailed reports and in the dashboard view. vCenter Update Manager supports mass remediation.

For detailed information about how to use vCenter Update Manager and how to orchestrate upgrades, see the vCenter Update Manager Administration Guide.