Cannot revert ESXi version when upgrading from 7.0 to 8.0

Products

• VMware vSphere ESXi

Issue/Introduction

• The rollback option to previous version is unavailable after upgrading to ESXi 8.0.
• You can choose the same build number when reverting ESXi version.
  
  For information about ESXi rollback, see Reverting to a previous version of ESXi 6.x, 7.x and 8.x

Environment

VMware vSphere ESXi 7.x
VMware vSphere ESXi 8.x

Cause

vCenter Server 8.0 is packaged with two FDM (Fault Domain Manager) VIBs for openssl-1.0.2 and openssl-3, and determines which VIB to be installed based on the ESXi versions: 

ESXi 7.0: fdm vib for openssl-1.0.2 will be installed
ESXi 8.0: fdm vib for openssl-3 will be installed

If the host is part of an HA cluster, upgrading to ESXi 8.0 and exiting the host from maintenance mode will install fdm vib for openssl-3 on the host.
This fdm vib installation discards the old (n-2) copies in altbootbank and retains only the (n-1) copies, so the option to roll back to an earlier version is lost.

Resolution

It is expected behavior.


Workaround

Disable vSphere HA before starting ESXi upgrade to prevent automatic fdm vib installation.
 

Additional Information

If you do not want to disable vSphere HA, config backup and restore can be used.

For information about ESXi host configuration backup and restore, see How to back up and restore the ESXi host configuration