So we have been talking about seamless upgrade. Following are the operations setup performs in order to ease the upgrade pain. Basically, the whole process of upgrading from BizTalk Server 2004 to BizTalk Server 2006 is divided in four steps:
In case of any unexpected failure while upgrading, we can resume the upgrade from the middle. To consider a scenario, let us say the machine being upgraded goes off the network while upgrading the remote databases. The upgrade can still be resumed from that stage by simply restoring the database that was being upgraded (from its backup) and executing the setup again.
Similarly, in case post upgrade configuration fails because of a similar reason, add a DWORD registry entry RerunUpgrade=1 under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\BizTalk Server\3.0_Migrated. The setup can be executed multiple times even after the BizTalk 2006 installation. This enables us to complete the upgrade successfully in case it fails because of some unprecedented scenario.