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Start Track 1 Datasets

1-4 User Reference

Use Pursuant to Company Instructions

Start Track 1 Datasets

Description A Start Track 1 dataset is a disk dataset that is defined by specifying the

number 1 (one) in the relative track field of the VSE EXTENT statement.

For example:

// DLBL MYFILE,’ANY.FILE’

// EXTENT SYS005,SYSWK3,1,0,1,20

In the above example, BIM-EPIC allocates 20 tracks to the MYFILE

dataset since the number 1 is in the relative track field. Using any other

number in relative track field indicates that BIM-EPIC will not handle the

allocation. The usual VSE JCL rules and requirements apply.

Start Track 1 datasets are only partially controlled. BIM-EPIC allocates

disk space for the dataset on output and will find the dataset on input.

However, no entry is made in the DSN Catalog, so no additional

information about the dataset is kept. You must supply the name of the

BIM-EPIC disk pool to use and the number of tracks or blocks to allocate

for the dataset. JCL supplies all remaining information.

A benefit of using Start Track 1 datasets is that the datasets do not need to

be entered in the DSN Catalog. However, Start Track 1 datasets require

significantly more I/O operations when opened, and only one version can

be kept on disk.

Because Start Track 1 dataset extents are not recorded in the DSN

catalog, BIM-EPIC must find the dataset extents in the VTOC. All

controlled datasets are written in pools, which can contain more than one

volume. For Start Track 1 datasets, this requires BIM-EPIC to read the

VTOC of every volume in the pool until it finds the dataset extents. This

activity occurs for both input and output. For output datasets, BIM-EPIC

deletes the previous version of a Start Track 1 dataset and then creates a

new Start Track 1 dataset. In contrast, BIM-EPIC only needs to read a few

records in the DSN Catalog to locate a cataloged dataset extent, no matter

where it is written, and multiple versions can be kept on disk.

Start Track 1 datasets are retained and scratched like uncontrolled

datasets. BIM-EPIC does not protect them from being deleted if their

expiration date has passed. You can protect the dataset from deletion by

using JCL, providing an expiration date or by indicating a number of days

before the dataset is expired. If you do not specify an expiration date,

BIM-EPIC provides the VSE default retention period of seven days.

To minimize overhead, Start Track 1 datasets should be cataloged to

improve performance, no matter how often the job is run.

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Memorex LOCK - VERSION 2-24 Informazioni Techniche Pagina 22