2 tape file concepts, File generations, Tape file concepts – HP NonStop G-Series User Manual
Page 41: Section 2, tape file concepts
DSM/Tape Catalog User’s Guide — 520233-008
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Tape File Concepts
DSM/TC manages tape files based on the information in their tape file entries. Some
data stored in the catalog is also stored in the label of a tape, but tape label information
is always secondary to DSM/TC information. If there is a conflict between the tape
label data and the DSM/TC database, DSM/TC satisfies or rejects a tape request
based on the information in its database.
DSM/TC rejects a request for an input tape file if the information in the catalog does
not exist or if it is inconsistent with the information given in the TAPECATALOG
DEFINE. For example, a requested tape file has expired, or you requested a
generation that does not exist.
A request for an output scratch tape is rejected if the pool you designate does not exist
or does not have entries with a status of scratch. In this situation, the operator can:
Create scratch tapes in the pool by changing the status of some tapes from
released to scratch or cataloging some new scratch tapes in the pool. $ZSVR
checks the pool every three minutes to see if a scratch tape is available.
Cancel the mount message with a REJECT TAPEMOUNT command.
To properly request tape files as input files, you must be familiar with a few concepts:
File Generations
Often an application runs on a daily, weekly, or monthly schedule that produces the
same cataloged tape file names on different volume sets. Their generation number
distinguishes these tape file entries from one another.
When cataloging a generation of a tape file, the generation number begins at one and
is automatically derived for the next generation by adding one to the generation
number of the last entry for the tape file. If you do not want automatic numbering, you
can specify a number in the CLASS TAPECATALOG DEFINE using the GEN attribute.
When you request a tape file that has multiple generation entries, DSM/TC issues a
mount message for the volume set of the latest generation unless you specify
otherwise in the GEN attribute of the TAPECATALOG DEFINE.
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