Rockwell Automation FactoryTalk Historian SE 3.0 UniInt Interface User Guide - Manual (Page 56)

Interface Disconnected Startup
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Interface

The interface must be built against UniInt version 4.3.0.x or later.

The interface node must have PI API version 1.6.1.5 or later installed.

The interface must not utilize the PI SDK to retrieve the extended point attributes
from the Historian Server.
Buffering
The interface node must have the Historian Buffering service installed and configured to
buffer data to prevent data loss while starting the interface in the disconnected startup
configuration when the host Historian Server is not available. Prior to the disconnected
startup feature, the interface could not start without a connection to the Historian Server
because the point configuration data needed to start the interface could only be retrieved
from the Historian Server. However, with disconnected startup, the interface receives point
configuration data from the cache files when no Historian Server connection is available. If
the buffering service is not running while the Historian Server is unavailable, the benefit of
being able to start the interface without a connection to the Historian Server is negated.
Moreover, any data collected while the connection to the Historian Server is unavailable
would be permanently lost.
There are two buffing services available; API Buffer Server and the Buffer Subsystem. API
Node buffering (BufServ) refers to functionality in the PI API that supports continuous
collection of data on an API Node regardless of the status of the destination Historian Server
or the network link to the Historian Server. The Buffer Subsystem (PIBufss) is a new
component of the FactoryTalk Historian System, primarily designed to enhance the High
Availability (HA) features of the Historian Server. PIBufss is different from the API Buffer
Server, even though it has most of the same capabilities and more.
The Buffer Subsystem offers significant benefits over the API Buffer Server, but does not
replace it entirely. PIBufss has advantages over Bufserv when connected to redundant
Historian Servers, configured as a Collective (Historian Server Replication) for High
Availability (HA). These Historian Servers must be running Rockwell Automation Platform
Release 1 (PR1) or a later version.
The PI API/BufServ 1.6.1.x introduced buffering to multiple Historian Servers from a single
machine. This includes buffering to replicated Historian Servers that are part of a single
Historian Collective. However, BufServ does not detect and validate the Historian Collective
configuration and as a result, requires manual configuration. Additionally, due to the
independent data compression taking place in the Snapshot Subsystem (at each replicated
Historian Server), BufServ does not guarantee identical records in the Historian Archive.
Detailed documentation for configuring and running API Node Buffering can be found in the
PI SDK Help (pisdk.chm, which embeds the piapi.chm file). The help file is located in the
PIHOME\PIPC\Help\ directory. The configuration details for the Buffer Subsystem can
be found in the Buffer Subsystem Help (pibufss.chm file).