Siemens SIMATIC PCS 7 Function Manual page 182

Failure, Switchover and Return of Fault-tolerant Components
6.4 OS server
● By automatically interconnecting the OS clients to the preferred server or to the available
● By generating process control messages in the message list.
The fault scenarios listed above and the resulting reactions by WinCC Redundancy are
described in the following.
Example configuration
Startup of an OS server pair
The following applies, in general: An OS server pair consists of the OS server and its OS
partner server. The two PCs are configured with WinCC Redundancy in a redundant grouping.
When the OS server pair starts up, WinCC Redundancy first checks which of the two OS
servers is to be assigned the master identification. This depends on which OS server starts
up first.
● If one OS partner server is active already when the other comes online, the second OS
● If no other OS server is active when an OS server starts up, it is assigned the master
The internal WinCC tag @RM_MASTER is set to identify the master OS server. The internal
WinCC tag @RM_MASTER is reset to identify the standby OS server.
182
OS server with master identification. The "@RM_SERVER_NAME" tag on an OS client
indicates the OS server to which this OS client is currently connected.
server receives the standby identification.
identification.
Fault-tolerant Process Control Systems (V8.0)
Function Manual, 03/2012, A5E02779471-02