This scenario is a migration upgrade. The migration upgrade is a managed transition rather than a strict upgrade. By using vMotion to move virtual machines directly from one production host to another production host, you minimize downtime of the virtual machines.

The following example provides a high-level overview of the upgrade process in an environment with ESX 4.0/ESXi 4.0 or higher and vCenter Server 5.5, using vMotion to migrate your running virtual machines to ESXi 5.5. The hosts in your environment must be licensed for and able to use vMotion.

You can perform a migration upgrade without vMotion. The only difference is the amount of downtime for the virtual machines.

A migration upgrade calls for sufficient resources to run the production environment partly on older hosts and partly on upgraded hosts. Any required redundancies and safeguards must be available on both upgraded and non-upgraded infrastructure during the transition.


  • Verify that one or more machines meets ESXi 5.5 requirements.
  • Verify that empty host storage is sufficient to hold a portion of your production virtual machines. Ideally, the storage is large enough to hold all of the migrated virtual machines. A larger capacity for virtual machines on this extra storage means fewer operations are required before all your virtual machines are migrated.
  • If your environment has vCenter Guided Consolidation, uninstall it.
  • Run the Host Agent Pre-Upgrade Checker. See Run the vCenter Host Agent Pre-Upgrade Checker.
  • Upgrade vCenter Server version 5.5. See Upgrading vCenter Server.

    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.

  • Install the version 5.5 vSphere Web Client. See Install or Upgrade the vSphere Web Client.
  • If your environment has vSphere Update Manager, upgrade it to the latest version. See Upgrading Update Manager.


  1. Use vMotion to move the virtual machines from the ESX 4.0/ESXi 4.0 or higher host.
  2. Upgrade the host to ESXi 5.5, or perform a fresh installation of ESXi 5.5.
  3. Add the ESXi 5.5 host to vCenter Server.
  4. Use vMotion to move the virtual machines that you removed from the ESX 4.0/ESXi 4.0 or higher host before the upgrade.
    For vMotion to work, the hosts must be managed by the same vCenter Server instance.

What to do next

For all hosts and virtual machines in the migration upgrade, take the following actions.

  • Upgrade your virtual machines. See Upgrading Virtual Machines and VMware Tools.
  • Upgrade your product licenses:
    1. Get your new license keys by email, or by using the license portal.
    2. Apply the new license keys to your assets using the vSphere Web Client).
  • Use the vSphere Web Client to upgrade the host datastore to VMFS5.

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