Siemens Simatic PCS 7 Function Manual page 221

Overview of the required tasks
NOTICE
Interrupted redundancy
Perform the steps described from Phase 1 to Phase 5 without extended interruptions because
the redundancy is not available during the update.
Upgrading Process Historian before the OS servers in runtime
You must first upgrade the Process Historian server to Process Historian 2014 SP2 (PCS 7
V9.0) before you:
● upgrade a PCS 7 plant to version PCS 7 V9.0 in runtime
● and simultaneously upgrade the operating systems of the OS servers, e.g. Server 2008
● or replace the hardware of the OS servers
You can only start upgrading the OS servers in runtime when the Process Historian is in the
"Active" operating state and all pending restorations have been executed.
Start the restoration multiple times, if necessary, if you still detect data gaps. You can start
the restoration manually in the management console or with the PH tray icon.
High Availability Process Control Systems (V9.0)
Function Manual, 05/2017, A5E39221836-AA
Failure, switchover and reintegration of high availability components
to Server 2012
7.10 Guide to updating a redundant OS in runtime
221