We are currently moving from sphere 5.1 to 5.5. In one of our instances we actually are moving the vcenter database instead of an upgrade. So we built out a new vcenter 5.5 and then simply upgraded and moved the vcenter 5.1 database to this instance.
The issue that is odd,is that we selected to "manually" upgrade the host agents. However after completion none of the hosts were disconnected in vcenter. So does that mean they didnt need a host agent upgrade? This seems a bit odd to me. Everything else is working fine though.