If you have standalone ESX 4.x/ESXi 4.x hosts, you can upgrade your hosts and the vSphere Client to upgrade your virtual machines. This scenario provides a high-level overview of the upgrade process when you do not have host clusters and you do not have vSphere Update Manager.

This scenario applies to your environment whether or not you have vCenter Server.

Verify the following details about your vSphere environment.

All your hosts must be ESX 4.x/ESXi 4.x or higher.

If your environment has vCenter Guided Consolidation, uninstall it before upgrading.


Run the vCenter Host Agent Pre-Upgrade Checker.

See Run the vCenter Host Agent Pre-Upgrade Checker.


If you have vCenter Server, upgrade to vCenter Server 5.1.

See Upgrading to vCenter Server 5.1.

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.

After the upgrade, the hosts are automatically connected to vCenter Server 5.1 if you select that option during the upgrade process.


Install or upgrade the vSphere Client to version 5.1. See Upgrade the vSphere Client

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


For all hosts, perform an interactive upgrade using an ESXi ISO installer image stored on a CD, DVD, or USB flash drive to upgrade ESX 4.x/ESXi 4.x. See Upgrading and Migrating Your Hosts and Upgrade or Migrate Hosts Interactively.

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 does not support rollback to the previous release.


Upgrade your virtual machines. See Upgrading Virtual Machines.


Get your license key either in email or by using the license portal.


Apply the new license keys to your assets using the vSphere Client.


Use the vSphere Client to upgrade your datastore to VMFS5.

See information about upgrading datastores to VMFS5 in the vSphere Storage documentation.