This document shows how to migrate an ESX host from the VMware ESX release 3.5 to VMware ESX 4.0, but it is valid for any ESX 3.x, It is designed for small environments, of one or two host's, but it would not make sense since it is a manual update process, without the ability to schedule the task or perform more than one simultaneous migration or by specifying a migration order for our hosts.

We continue in the process of migrating the VMware Virtual Infrastructure environment 3 to VMware vSphere 4. We first upgraded the VMware VirtualCenter server to VMware vCenter Server, later we will have migrated the VMware Update Manager component to VMware vCenter Update Manager 4.0. After this, we will now be able to upgrade from ESX to the 4.0. All this, of course, taking into account whether our ESX hosts are fully compatible with the new version, to do this, check it in the VMware HCL.