Changing an NSX Upgrade Host Group to parallel generates an error "should not be upgraded in parallel"

Products

• VMware NSX

Issue/Introduction

• On the NSX UI, System> Upgrade NSX > Hosts> Actions> Change Upgrade Order, selecting 'Parallel' on Upgrade Order generates the following error: 
  
  "Group 'Group for xx-xx-xxxx-xxxxx' should not be upgraded in parallel, since two or more hosts belonging to a cluster could be placed in maintenance mode at the same time."

  

Environment

VMware NSX

Cause

Parallel Upgrade Order is not supported for Hosts Groups configured for maintenance mode upgrade. Parallel mode is supported for in-place upgrades. 

Resolution

VMware NSX is working as designed.

The only options that can achieve parallel upgrade of hosts within a cluster are as follows:

Option 1 - Non-vLCM/Non-VSAN cluster
In a non-vLCM and non-VSAN cluster, hosts from a vSphere cluster can be added to different Host Upgrade Unit Groups.
These Host Upgrade Unit Groups can be configured to upgrade in parallel thus allowing hosts within a single cluster to upgrade in parallel.

or

Option 2 - In-place Upgrade
The cluster can be changed from maintenance mode upgrade to in-place. 
On the NSX UI, System> Upgrade NSX > Hosts> Actions> Change Upgrade Mode, select 'In-place'.

Additional Information

Refer to the section "Limitations on -In-place Upgrade" documented in the Operational Impact of the NSX Upgrade