gtpd1m26Database Reference

Database Archives

This section provides information about the TPFCS database archive services.

External Device Support

External device and archiving support provide interfaces that will allow you to read and write data from external devices such as tape, general data sets, communication devices, and any other devices supported by the TPF 4.1 system. The initial support will be for tape only. As part of the external device support for tape, functions have been added that will interface with the tape robotics to allow access to tapes without operator intervention. Through the support for tape and tape robotics, external device support will be used to provide an archiving function that will be used by TPFCS to archive collections. Through the use of tape robotics and archiving, TPFCS will be able to move collections in and out of the TPF 4.1 system as required.

Archiving Support

For archiving, the application calls the TPFxd_archiveStart function. The TPFxd_archiveStart function will return a token that the application passes to TPFCS as a parameter on the TO2_capture or TO2_restore function. Once the request has completed successfully, the application can continue with another TO2_capture or TO2_restore function request until all required collections have either been archived or restored from the archive devices. The application will then issue a TPFxd_archiveEnd function request. Therefore, the application program determines if the TPFCS request is for archiving or to just restore another external device.

Capture and Restore Support

TPFCS provides functions to write and retrieve collections to external storage. By using these TPFCS functions and the archiving support of the external device support, collections will be able to be moved in and out of archived storage.

The TO2_capture and TO2_restore functions are used to write and retrieve collections from the external device using the external device support functions.

When an application decides to capture or restore a collection, the application must choose which external device will be used for the function. The application starts a capture or restore by issuing a TPFxd_externalStart function call with the required values. This function call will return a token that the application passes to TPFCS as a parameter on the TO2_capture or TO2_restore function. Once the request has been completed, the application issues a TPFxd_externalEnd function call to inform the external device support that it is done.

When TPFCS captures a collection to external storage, it will precede the collection with a capture header object and it appends a capture trailer object to the captured collection. Therefore, the captured object will start with a header object and end with a trailer object. Between the two objects, there will be the actual collection being captured. The captured object will be written as a set of control information and 4-KB data records. For each set of data records, there will be a data trailer object to indicate the end of one set of data records from another set of data records. Figure 10 shows an example of data on the external device.

Figure 10. Data on an External Device


If the collection is small enough to fit in the object control information area, the capture trailer object will follow the object control information.