Siemens Simatic PCS 7 Function Manual page 220

Failure, switchover and reintegration of high availability components
7.10 Guide to updating a redundant OS in runtime
Initial situation
● Server_1 is master server.
● Server_2 is standby server.
● Client_1 is connected to Server_1 because this server is configured as its preferred server.
Client_1 represents all OS clients connected to Server_1.
● Client_2 is connected to Server_2 because this server is configured as its preferred server.
Client_2 represents all OS clients connected to Server_2.
Requirements
● Process Mode of the Maintenance Client was ended before the ES was updated.
● The update of the PCS 7 project for the ES is complete.
● If the Maintenance Station is used, SIMATIC PDM is installed on the ES.
● All the settings for the configured mode have been made. The configuration data has been
loaded onto the ES from NetPro.
● If you want to use encrypted communication after the software update: "Encrypted
communication" is activated for the ES with migration mode. You can find information about
this in the documentation
● All OS servers and all OS clients are running with PCS 7 V8.0 or higher.
Note
If a Process Historian is used in the Plant, it has to be updated, be in the state "Active" and all
recoveries have to be finished first, before any OS Server is stopped. Otherwise some data
gaps might not get closed after the migration is done.
220
Process Control System PCS 7; PCS 7 PC Configuration .
High Availability Process Control Systems (V9.0)
Function Manual, 05/2017, A5E39221836-AA