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External volumes checked in to Control-M/Tape sometimes have the same volser as a volume already in the Control-M/Tape Media Database. This is problematic because the volser must be a unique identifier of a volume in the Media Database. To solve this problem, Control-M/Tape uses two fields, VOLSER and SL-NAME (Standard Label Name) to identify volumes in the Media Database.
Table 26 VOLSER and SL-NAME
Volume Identifiers |
Description |
|---|---|
VOLSER |
The VOLSER field is used to enter the logical volser in the Media Database. This is the unique volser assigned to the checked-in volume. When a volume is checked in, the value in the VOLSER field is used to identify and access the volume (for example, in JCL references, job statements, references in the MVS catalog, and mount messages). A logical volser can be automatically generated with the prefix specified in the EXTRNVOL installation parameter, or it can be specified manually in the External Volume Check-In screen. Assigning a unique logical volser does not affect the physical (internal) label on the volume in any way. |
SL-NAME |
The physical volser (Standard Label name) is stored in the SL-NAME field of a volume record. For local volumes, the SL-NAME and VOLSER are the same. For external volumes, the SL-NAME is used to reconcile the discrepancy between the requested volser, and the mounted volume’s standard label, when they do not match. |
When an external volume is checked in, a new logical volser is used to identify the volume. In addition, the original volser (on the volume’s internal label) is stored in the SL-NAME field.
When a job requests a specific volume through a JCL statement, the operating system checks that the volser on the volume’s internal label matches the requested volser.
If the requested volume and the internal label do not match, the operating system would normally reject the tape. However, when a volume is defined to Control-M/Tape with different values in the VOLSER field and the internal label, Control-M/Tape intervenes in the operating system processing. If the value in the SL-NAME field matches the volser in the internal label, Control-M/Tape forces the operating system to accept the volume.
Note: The special handling described above is supported only when tapes are accessed through a READ function. If a tape with a duplicate name is opened for WRITE access, the internal label of the tape (volume) is changed so that it matches the external name of the volume.
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