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 more 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 a VIB to be installed on the ESX host depending on ESXi versions: 

fdm vib for openssl-1.0.2 is installed in ESXi 7.0.
fdm vib for openssl-3 is installed in ESXi 8.0.

If the host is part of an HA cluster, upgrading to ESXi 8.0 and removing the host from maintenance mode will install fdm vib for openssl-3 on the host.
The 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 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 more information about ESXi host configuration backup and restore, see How to back up and restore the ESXi host configuration