Occasionally, an issue or bug will require admins to revert to a previous build or version of ESXi. In the event you patch your hosts (as opposed to fresh installs), it is possible to rollback to a prior installed version via the GUI. Rollbacks should not be taken lightly. If you are reverting in a production environment, discuss options with support first.

A few housekeeping items before we jump into the rollback process.

Compatibility – If you are leveraging new features introduced in vSphere 6.5, ensure you check compatibility against vSphere 6.0. Two main features to be cognizant of when reverting from 6.5 to 6.0 are VMFS and virtual machine hardware versions.

  • VMFS 6: VMFS 6 was introduced with vSphere 6.5. However, vSphere 6.0 utilized VMFS 5. If you created a VMFS 6 version with ESXi 6.5, you will not be able to access the datastore after rollback.
  • VM Hardware Version: vSphere 6.5 also introduced version 13 virtual machine hardware. Version 13 hardware is not compatible with ESXi 6.0. Version 11 or lower is compatible.  However, there are a few supported options for downgrading virtual machine hardware versions.

Back Up Host Configuration – Before making any changes, back up the ESXi Configuration.

Downgrade ESXi 6.5 to 6.0

To begin put the host into maintenance mode, ensuring VMs are powered off or migrated away from the host.

Enter Maintenance Mode

Next, open a console to the ESXi host. From the DCUI screen, hit F12 to select shutdown options.

DCUI Shutdown Options

From the Shut Down/Restart screen, hit F11 to restart the host.

Restart ESXi

Once ESXi begins to load, hit Shift+R to access Recovery Mode.

ESXi Recovery Mode

Select Y to roll back. This is a permanent endeavor. Meaning, once you have rolled back, you will no longer have the option to boot into the newer version.

Hypervisor Recovery

ESXi will now revert to the previous version. Once ESXi has rolled-back and booted, verify the correct version has loaded.

ESXi 6 Recovery

Navigate back to vCenter. If the host did not re-connect, manually Connect the host.

Connect Host

Lastly, Exit Maintenance Mode.

Exit Maintenance Mode

VMware KB – Revert ESXi to a Previous Version

Closing Thoughts – If you can’t restart the host to check Recovery Mode for a previous version, you can check the boot banks for additional builds.

Check for ESXi Rollback Version via SSH

SSH to the host in question and run the command to check to primary and secondary boot bank.

tail -2 /*bootbank/boot.cfg

Bootbank Config

As we can see here, the primary boot bank contains ESXi 6.5 code and the alternate boot bank contains ESXi 6.0 code.

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