In connection with file name-oriented tape processing, MAREN BS2000 commands are offered for working with the MAREN TFT (Task File Table). The commands are offered in the SDF menu under the application domain STORAGE-MANAGEMENT.
Functional description
When accessing a tape file that is not contained in the TSOSCAT file catalog, the tapes belonging to this file can be determined from the MAREN catalog.
This is only possible if the system on which the tape file was created and the system on which it is to be further processed both use the same MAREN catalog. The information required for file assignment concerning the tapes to be used and their device type is located in the MAREN catalog and can be called from there. Manual specification of the archive number and their device type is no longer necessary, with the result that the assignment of a tape file TAPE.FILE now looks simply like this:
/IMPORT-FILE SUPPORT=*TAPE(VOLUME=*ANY,DEVICE-TYPE=*ANY,FILE-NAME=TAPE.FILE)
DMS processes such a command and pass the file name on to MAREN. If the MAREN catalog contains entries with this name, MAREN returns the archive number and device type of the tapes marked in these MAREN catalog entries to DMS (“volume substitution”). Using the information received from MAREN, DMS can complete the file assignment and request the required tapes.
One problem that can arise in connection with volume substitution is that the same file name may occur more than once in the MAREN catalog. This is the case if the same tape file was created at different times and using different tapes, and if the relevant tapes in the MAREN catalog have not yet been released. These individual versions of a file are not distinguished by the file name. By default, MAREN can select the latest (youngest) file version. But it must also be possible to address an older file version.
Another potential problem lies in the fact that tape files cannot always be uniquely assigned to user IDs. This means that there may be several entries in the file catalog (TSOSCAT) for the same tape file in the Data Management System. For example, the two file names $USERA.TAPE.FILE and $USERB.TAPE.FILE may refer to the same file on the same tape. For this reason, BS2000 tape management only stores the max. 41-character file name without the user ID in the tape labels (HDR3 label) and, for the same reasons, the tape file names are not given user IDs in the MAREN catalog.
Volume substitution encounters problems at the latest when the file name involved has several entries in the MAREN catalog and the associated tape files were created under different user IDs. Selection based on the file version does not always provide a solution here, as the different tape files with the same name may easily refer to files with completely different contents (e.g. file $A.XY contains inventory data, and file $B.XY contains personnel data).
Selection of a specific file version and specification of which user IDs have to be taken into account are handled by means of the command ADD-MAREN-FILE-ENTRY.
In the context of volume substitution the VERSION operand determines which file version in the MAREN catalog is accessed in a subsequent IMPORT-FILE command (with VOLUME=*ANY) and thereby which archive numbers are required for processing.
The USER-IDENTIFICATION operand determines whether only MAREN catalog entries from the user’s own or from a foreign user ID are to be evaluated when determining this volume serial number. It should be borne in mind in this context that only the MAREN catalog entries of shareable tapes (with USER-ACCESS=*ALL-USERS or *FOREIGN-READ-ONLY) of foreign user IDs can be evaluated.
The decision made by way of ADD-MAREN-FILE-ENTRY is stored in a task-specific table, where it is chained to any entries created in earlier ADD-MAREN-FILE-ENTRY commands and subsequently evaluated in the course of volume substitution. This MAREN-specific file table, known as the MAREN TFT (Task File Table), is created when the ADD-MAREN-FILE-ENTRY command is first entered and deleted at the latest when the task is terminated (EXIT-JOB command). This table contains only one entry for a given file name, i.e. if a file name already entered in the MAREN TFT is used in an ADD-MAREN-FILE-ENTRY command, the values stored there for the VERSION and USER-IDENTIFICATION operands are replaced by the current values.
Entries in the MAREN TFT can also be explicitly deleted from this table. This is done using the REMOVE-MAREN-FILE-ENTRY command.
Information on the entries in the MAREN TFT can be requested using the SHOW-MAREN-FILE-ENTRY command. The information displayed can refer to all entries in the MAREN TFT or to one specific file name.
Overview
| BS2000 command | Meaning |
| ADD-MAREN-FILE-ENTRY | Adds an entry to the MAREN TFT |
| REMOVE-MAREN-FILE-ENTRY | Removes an entry from the MAREN TFT |
| SHOW-MAREN-FILE-ENTRY | Outputs information from the MAREN TFT |