The only ESX 2.x version that has upgrade support is ESX 2.5.5, though support is limited for this type of upgrade. VMware supports upgrades from ESX 2.5.5 under certain conditions.

When you upgrade from ESX 2.5.5 to ESX 4.0, you can perform a migration upgrade with or without VMotion. In a migration upgrade, you migrate ESX 2.5.5 virtual machines to ESX 4.0 hosts, as follows: Evacuate the virtual machines from the ESX 2.5.5 host. Do a fresh install of ESX 4.0. Migrate the virtual machines back to the newly installed ESX 4.0 host. See Upgrading by Moving Virtual Machines Using Upgrade VMotion.

Direct, in-place upgrade from ESX 2.5.5 to ESX 4.0 is not supported, even if you upgrade to ESX 3.x as an intermediary step. The default ESX 2.5.5 installation creates a /boot partition that is too small to enable upgrades to ESX 4.0. As an exception, if you have a non-default ESX 2.5.5 installation on which at least 100MB of space is available on the /boot partition, you can upgrade ESX 2.5.5 to ESX 3.x (ESX 3.0.2 or higher) and then to ESX 4.0 Update.

The upgrade of ESX 2.5.5 to ESX 3.x requires the use of one of the following methods:

Graphical upgrade from CD

Text-mode upgrade from CD

Tarball upgrade using the service console

Scripted upgrade from CD or PXE server using esxupdate

Scripted upgrade from CD or PXE server using kickstart commands

For information about these upgrade methods, see the VMware Infrastructure 3 documentation.