Siemens SIMATIC PCS 7 Function Manual page 198

Failure, Switchover and Return of Fault-tolerant Components
6.4 OS server
WinCC project is deactivated
A functionally equivalent WinCC project is activated on both OS servers. If the WinCC project
is deactivated on OS Server 1 (master identification), WinCC Redundancy triggers the
following reactions:
● OS Server 2 (standby identification) saves the time of the failure (date and time of day) of
OS Server 1 (master identification).
● OS Server 2 reports the failure of OS Server 1 with a process control message in the
process control list.
● OS Server 2 now takes over the role of the master by setting the @RM_MASTER tag. The
@RM_MASTER_NAME tag is changed accordingly.
● If the WinCC project is activated again on OS Server 1, OS Server 1 is set as the standby
and the @RM_MASTER tag is reset. The @RM_MASTER_NAME tags are changed
accordingly.
Gaps in the archive data occur on OS Server 1 during the time it is inactive. As soon as OS
Server 1 returns, the gaps in the data are remedied by the following measures:
● OS Server 2 saves the date and the time of day, marking the return of OS Server 1.
● OS Server 2 reports the return of OS Server 1 with a process control message in the
message list.
● The data gaps in the message, process data and user archives of OS Server 1 are filled
by the data from the OS Server 2 memory. Conditions: The options "Synchronization of
Tag Logging after the partner server comes back online" and "Synchronization of Alarm
Logging after the partner server comes back online" must be enabled in the "Redundancy"
dialog box for this.
● The @RM_MASTER tags remain unchanged in both servers:
– OS Server 2 keeps the master identification.
– The @RM_MASTER tag remains set.
– The @RM_MASTER tag for OS Server 1 is reset.
Disrupted network connection to the OS partner server
A disrupted network connection is only detected in the redundancy scheme when:
● There is a fault in the spur line.
● There is a defective connector or network adapter.
● A PC station is identified as faulty.
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Fault-tolerant Process Control Systems (V8.1)
Function Manual, 11/2014, A5E34878832-AA