Limitations of disconnected startup

Known limitations imposed on an interface running with disconnected startup enabled include extended attribute length, using PI SDK, and suspended output point updates.

Extended attribute lengths

To maximize the functionality of the disconnected startup configuration, the use of Data Archive version 3.4.370 or later is recommended. Data Archive version 3.4.370 or later in conjunction with PI API version 1.6.1.x or later provides greater field lengths for the tag, descriptor, exdesc, instrumenttag, and pointsource attributes. Moreover, PI SDK is no longer required for support of the increased field lengths.

The following table lists the maximum field lengths for a given PI point attribute for the version of Data Archive used. In all cases, the PI API version is assumed to be 1.6.1.x or later to support disconnected startup.

Maximum attribute lengths

Note: If the actual data stored for the point attribute is greater than the maximum field length specified in the table, the returned value for the attribute is truncated to the maximum length for the given Data Archive version.

Interfaces using PI SDK

The disconnected startup feature utilizes PI API to retrieve extended point information from Data Archive that is stored in the necessary caching files. Disconnected startup is not supported if PI SDK is required for the interface to start. The operational need for PI SDK is interface-specific. Interfaces supporting disconnected startup will explicitly say that disconnected startup is supported in the Supported Features table of the interface manual.

In the case where the interface supports disconnected startup, uses PI SDK by default to retrieve extended point attribute information, and Data Archive is earlier than version 3.4.370, you must define the /pisdk=0 parameter to disable PI SDK before enabling disconnected startup. For cases where Data Archive is later than version 3.4.370, the interface always uses PI API to retrieve extended attribute information and does not require disabling PI SDK.

For more information about enabling and disabling PI SDK, see Enable PI SDK.

Suspended output point updates

The interface can start and run in the disconnected startup configuration while Data Archive is unavailable. However, outputs will not function while disconnected from Data Archive. Once the interface establishes a valid connection, outputs from Data Archive to the interface resume normal operation.