OpsMgr R2 RTM: upgrade paths and -tasks

The Upgrade Guide – online version to be found here - contains valuable information about what kind of upgrade paths to OpsMgr R2 RTM are supported.

When in doubt about a certain upgrade path, post your question on the OpsMgr Online Forum BEFORE starting the upgrade. http://social.technet.microsoft.com/Forums/en-US/category/systemcenteroperationsmanager

From OpsMgr SP1 to R2 RTM
When the OpsMgr environment is at SP1 level you can upgrade directly to R2.

From OpsMgr RTM to R2 RTM
Sometimes I bump into OpsMgr environments which are still at RTM level. These environments can't be upgraded directly to R2. First SP1 needs to be applied before an upgrade to R2 is possible.

From OpsMgr R2 RTM Eval to R2 RTM
You can upgrade directly to R2 RTM full version.

From OpsMgr R2 RC Select R2 RTM Eval
Not possible. Wait for the R2 RTM Select to perform an inplace upgrade. Look here for the information from the community.

Diagram of available upgrade paths
 
Tasks to be completed BEFORE the upgrade

• A valid backup of the of the OpsMgrdatabases.
  (OpsMgr, DW & MasterDB, it contains entries for SCOM)
  .
  
• Backup EncryptionKey (write down the password!).
  
  
• Export Unsealed MPs.
  
  
• Remove Agents from Pending.
  
  
• Increase available space for data and logfiles of SCOMDBs to 50% or more.
  
  
• Remove Agents from systems with standalone consoles.
  
  
• Remove Agent from the SRS server hosting the OpsMgr reports.
  
  
• Disable notification subscriptions.
  
  
• Disable Connectors (if applicable).
  
  
• Write down all usernames and passwords used by OpsMgr for ‘just-in-case’.
  (Action, SDK, DW Read, DW Write)

Speeding up the upgrade
Nice thing is to run a stored procedure on the SQL-server hosting the SCOM-databases, which will speed up the upgrade process: 
Running upgrade using RDP connections
When the upgrade is done on the servers through a RDP session it is important to run it with the switches which makes it a Console session. Otherwise the logfiles – made during the upgrade – will be lost when the system restarts.

• Windows 2003 / XP: mstsc.exe /console
• Windows 2008 / Vista / 7: mstsc.exe /admin

Upgrade order

1. RMS
2. Reportingserver (performed on SRS server, remove OpsMgr Agent when present).
3. Standalone OpsMgr Consoles
4. Management Servers
5. Gateway Servers
6. Agents
7. WebConsole

And - if applicable - the ACS Collector with the ACS-database

Special thanks to Graham Davies who warned for some pitfalls.