Things to be kept in mind.
1. Make sure to plan for the proper amount of downtime , as the upgrade can take several hours to complete.
2. If you start the upgrade process, please login to CLI and check to see if there is a banner indication that the upgrade is in progress and not to make any config changes.
3. If ClearPass says the upgrade is in progress, DO NOT REBOOT, DO NOT RESTART SERVICES.
4. For major upgrades, the upgrade does not officially start until the server is rebooted. After it is rebooted, the web UI MAY come up and may show that there is no license or no configuration or both. THIS IS NOT A SIGN THAT THE UPGRADE NEEDS TO BE INTERRUPTED. This means that the configuration has not yet been restored. Doing a restore operation during upgrade can be the most time consuming part. Please let it do its work during this time. You can check on its status by logging in to the CLI and looking for the upgrade in progress banner.
Please call Aruba TAC if the you feel that the upgrade is stuck and do not INTERRUPT the upgrade procedure.
This article is published because multiple related issues are seen.