How to Automate the Upgrade of Classic ESX 4.x to ESXi 5

In prior releases of ESXi, there was not a supported method of upgrading from classic ESX to ESXi, you had to perform a clean installation. With the release vSphere 5, ESXi is the only available option and providing a supported and easy method for migrating to ESXi will be very helpful for users. There are currently three options of migrating/upgrading from ESX 4.x to ESXi 5. Going forward in the future, two additional methods will be available for upgrading ESXi 5.x to subsequent update/patch releases.

Here is a table of the supported ESXi 5 upgrade options:

The first two options should be pretty straight forward and I won't go into any details, but if you are interested, check out Ivo Beeren's post here. If you decide to use VUM to perform you upgrade, make sure you check out this post about lopsided bootbanks before doing so. The 3rd option is a new feature in a kickstart installation and you now can specify two additional types of installation:

• upgrade - Tries to perform an upgrade from ESX(i) 4.x to ESXi 5.x
• installorupgrade - Tries to perform an upgrade from ESX(i) 4.x to ESXi 5.x, if it fails, it will perform a clean installation

In addition to the new installation types, there are two new options that can be specified:

• --deletecosvmdk - If the system is being upgraded from ESX, remove the directory that contains the old Service Console VMDK file, cos.vmdk, to reclaim unused space in the VMFS datastore
• --forcemigrate - If the host contains customizations, such as third-party VIBS or drivers, that are not included in the installer .ISO, the installer exits with an error describing the problem. The forcemigrate option overrides the error and forces the upgrade

Here is an example of kickstart specifically for upgrading from ESX 4.x to ESXi 5:

Note: One thing I noticed from the upgrade is that even if you specify a new root password, the current password is still preserved. Virtual machines located on local VMFS volumes will also be preserved as long as you do not use the --overwritevmfs option

You will also know that an ESXi 5 host was upgraded from ESX 4.x when you login to ESXi Shell, a motd will display a message.

As you can see you have several options of upgrading both ESX(i) 4.x to ESXi 5, though if you have a choice between an upgrade and reinstall, my personal preference would still be a clean installation via kickstart or host profiles.