Memorex LOCK - VERSION 2-24 Dokumentacja Pobierz pdf (Strona 18)

Start Track 1 Datasets BIM-EPIC Fundamentals

1-4 User Reference

Start Track 1 Datasets

A Start Track 1 dataset is a disk dataset that is defined by the use of the number “1” in the

relative track field of the VSE EXTENT statement. For example:

// DLBL MYFILE,’ANY.FILE’

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

The use of the number “1” in the relative track field above indicates that BIM-EPIC will

allocate the dataset. The use of any other number in this field indicates that BIM-EPIC does

not handle the allocation.

Start Track 1 datasets are only partially controlled. BIM-EPIC allocates disk space for the

dataset on both input and output. However, you supply the name of disk pool to be used and

the number of tracks or blocks to allocate for the dataset. All information is supplied by JCL.

Start Track 1 datasets provide one benefit: the dataset does not have to be entered in the DSN

Catalog. However, they are less efficient than DSN Catalog datasets and they provide limited

control over retention.

Start Track 1 datasets also require more I/O operations when they are opened. Because a Start

Track 1 dataset’s extents are not recorded in the catalog, BIM-EPIC must find the dataset’s

extents from the VTOC. In addition, all controlled datasets are written in pools, and pools can

contain more than one volume. BIM-EPIC must read the VTOC of every volume in the pool

until it finds the dataset’s extents. This is true for both input and output. BIM-EPIC deletes

any previous version of a Start Track 1 dataset before creating a new one. BIM-EPIC must

search on output to locate and delete the old version.

In contrast, BIM-EPIC only needs to read a few records in the DSN Catalog to locate each

extent of a cataloged dataset, no matter where it is written.

Start Track 1 datasets are retained and scratched like uncontrolled datasets. BIM-EPIC does

not protect them from being scratched, and only one version can exist at a time. To retain the

dataset using JCL, specify an expiration date or the number of days. If you do not specify an

expiration date or Days Retention, BIM-EPIC provides a default retention of seven days.

Because of the limitations on retention, Start Track 1 datasets are useful only for work

datasets. Because of the overhead required for these datasets, even a work dataset in a

frequently run job should be cataloged to improve performance.

Start Track 1 datasets are affected by the AUTOCAT, CATRT1, MINRET, NCATDSK, and

STRTRK configuration options. In addition, they can be affected by other configuration

options that apply to disk. See the BIM-EPIC Installation and System Guide for further

information.

Description

Configuration

Options

1 2 ... 13 14 15 16 17 18 19 20 21 22 23 ... 488 489

Brak uwag

Memorex LOCK - VERSION 2-24 Dokumentacja Strona 18