Hi
A restore makes sense but it is not in the steps (the restore is only mentioned for step 2 (upgrading from vCenter Server 5.0 to vCenter Server 5.1 Update 1) not step 3:
Upgrading the Primary Server Continuation of the upgrade process assumes the upgrade of the Secondary server completed successfully.
Procedure 1 You have the following options: ■ If you are upgrading from vCenter Server 5.0 to vCenter Server 5.1 Update 1, continue with Step 2. ■ If you are upgrading from vCenter Server 5.1 to vCenter Server 5.1 Update 1, go to Step 3.
2 Before proceeding with the upgrade procedure, perform a restore of the vCenter Server database, Single Sign-On database, VMware Update Manager database, and SSL certificates that were backed up at Step 4 on the Secondary Server.
3 Change the server role to Primary/active:
a Launch the vCenter Server Heartbeat Configure Server wizard and click the Machine tab. Change the server role for the current (Primary) server to Active and click Finish.
b Using the Service Control Manager, start the VMware vCenter Server Heartbeat service.
c Using the vCenter Server Heartbeat Console, verify that all status icons on the Server: Summary page are green indicating that the Start process has completed and all protected services are started. d Using the Service Control Manager, stop the VMware vCenter Server Heartbeat service.
4 You have the following options:
■ If you are upgrading from vCenter Server 5.0 to vCenter Server 5.1 Update 1, go to Step 6.
■ If you are upgrading from vCenter Server 5.1 to vCenter Server 5.1 Update 1, continue with Step 5.
5 Upgrade Single Sign-On
a Start VMware vCenter Installer for the version you want to upgrade to and select VMware vCenter Single Sign On from the list.
b Proceed with the installation.
c In the event that errors are encountered during the upgrade process, research the cause of the upgrade. If the issue can be resolved then it is safe to proceed with the upgrade procedure.
6 Start VMware vCenter Installer for the version you want to upgrade to and select VMware vCenter Inventory Service from the list.
7 When prompted, select Do not overwrite. Leave my existing database in place.
8 From the VMware vCenter Installer for the version you want to upgrade to, select vCenter Server from the list.
the rest continues on page 63 I have checked 4 different upgrade documents for earlier versions and they all show more or less the same steps.