Rockwell Automation FactoryTalk Historian SE 3.0 H2H Interface User Guide - Manual (Page 25)

FactoryTalk Historian To Historian Interface User Guide 19
number of tag edits are made, a user may choose to restart the interface. Restarting the
interface will force it to process all edits by rebuilding its tag list.
Error Handling
When the interface encounters an error, it will print a message to the log file. If the error is
tag-specific, the error message will include the tag name along with the specific error code.
The tag is then marked by the interface as being in error and removed from the update list.
The interface will attempt to clear tags in error every 10 minutes. It does this by trying to read
a value from the source tag and then update the interface tag with that value. If this is
successful, the tag is added back to its assigned scan class for data collection. Otherwise, it
remains in error until the next attempt to clear it.
If an error is not tag-specific, the interface verifies server connectivity. Typically system
errors are a result of network upsets. When a system error is encountered, the interface
verifies Historian Server communication and attempts to continue collecting data.
Source Historian Server-Level Failover
Source Historian Server-level failover maximizes interface data availability on the receiving
Historian Server. It requires that two Historian source servers are available that have identical
tag definitions and data streams for interface points. This requirement ensures the interface
will obtain the same data regardless of which source server is active. Source Historian Server-
level failover is not supported for Historian 2.
Failover is enabled by specifying a primary and secondary source server in the interface
startup file. On startup the interface attempts to establish a connection to each source server
then load and initialize its tag list. Data collection begins from the primary source server
making it the active node while the secondary source server assumes the standby role.
However, if one of the source servers is unavailable on startup, the other server is designated
the active source regardless of primary or secondary configuration.
Note: Source tag mapping by point ID is not compatible with server-level failover.
This is because there is no guarantee of a point ID match between two source
Historian Servers unless they are part of a Historian Collective.
Fault Conditions
There are two conditions that will cause the interface to initiate failover: a communication
failure or detection of stale data.
Communication Failure
The first failover condition is when the interface loses communication to the active Historian
source server. This may be the result of a temporary network upset, shutdown of the active
source server, hardware failure, etc. The interface has no way of identifying what causes the
disconnection. A disconnection means the interface did not receive a response from the active
source within the timeout period. The interface may initiate a short wait then attempt to
reconnect to the active source before attempting to failover. The timeout period, pause