Memorex LOCK - VERSION 2-24 Informacje Techniczne Pobierz pdf (Strona 454)

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101

Dataset Fragmentation

13-2 User Reference

Use Pursuant to Company Instructions

Datasets

Dataset Fragmentation

Description When you create a dataset with a large primary allocation, there may not

be enough contiguous free space in the pool to contain the entire primary

allocation. BIM-EPIC responds to this condition by allocating the largest

amount of contiguous free space to the primary extent and allocating

secondary extents, as necessary, when the primary extent becomes full.

This process is called dataset fragmentation.

Automatic dataset fragmentation can be enabled globally by specifying

the configuration option FRAG=YES. Dataset fragmentation can be

enabled for an individual dataset by:

 Specifying option code F on a DLBL statement

 Specifying the MXIG subparameter or ALX subparameter in the

SPACE parameter on a DD statement

 Allowing the operator to respond with the FRAG command to the

EP038 message

Secondary

Allocation

BIM-EPIC automatically allocates secondary extents to eligible datasets

when the primary extent has been filled.

Secondary extent allocations are not available for direct access or

TYPEFLE=WORK datasets. Secondary extent allocations are available

for SORTWK datasets only if the SORT program being used specifically

allows it.

For cataloged datasets, you can specify the size of the secondary extents

and a maximum number of up to 255 secondary extents. If you use DD

statements for your disk datasets, the size of the secondary extents can be

specified in the SPACE parameter with the maximum number of

secondary extents specified in the VOLUME parameter. If you do not

define a secondary extent allocation requirement using one of these

methods, BIM-EPIC automatically allocates up to 255 secondary extents.

Each extent will be one-half the size of the primary extent.

Truncation At close, any allocated extent that was not completely filled can be

truncated so that the unused portion of the extent is freed. BIM-EPIC

performs truncation for controlled datasets by altering both the VTOC

and the DSN Catalog to show only the space actually used. Extents are

always truncated on track or control interval boundaries.

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