Memorex LOCK - VERSION 2-24 Technické informace stáhnout pdf (Strana 62)

100

101

Using Disk Processing

1-44 User Reference

Use Pursuant to Company Instructions

BIM-EPIC Disk Processing

Using Disk Processing

Description The tasks performed for disk open, close, and end-of-extent processing

are similar to the tasks performed for tape processing. For disk

processing, BIM-EPIC must make the space allocation, which is more

complicated than finding the correct tape volume.

Quick Disk

Allocation

(QDAS)

During every open process, VSE reads the VTOC sequentially, which can

require thousands of I/O operations. BIM-EPIC provides the Quick Disk

Allocation System (QDAS) which dramatically decreases the time

required to allocate an output dataset.

QDAS maps disk volume free space to virtual storage. One map is created

for each QDAS-controlled volume when the BIM-EPIC is initialized.

When disk space is used or freed for any controlled dataset or

uncontrolled dataset, QDAS updates the map in storage.

Note:Note:

QDAS updates the maps only when the VTOCs of the disk volumes under

its control are updated using the VSE common VTOC handler

($IJJHCVH). Programs that update the VTOC directly may bypass the

QDAS interface and cause the maps to get out of sync with the VTOC.

This applies to a very limited number of programs, such as DITTO.

However, should this condition occur, you can refresh the QDAS map

tables at any time. See Chapter 4 of the BIM-EPIC Installation and

System Guide for additional information.

Because QDAS maps free space, you must refresh the map tables daily to

reallocate the space made available by expired Start Track 1 files. This

refresh is not necessary if the disk files are catalog controlled. It is

recommended that this procedure be performed as part of the BIM-EPIC

daily maintenance procedures which should occur after midnight. See the

BIM-EPIC Installation and System Guide for additional information.

The following events occur on output.

 BIM-EPIC locates the pool where the dataset is assigned. For

cataloged datasets, BIM-EPIC locates the pool in the DSN

Catalog entry. For Start Track 1 datasets, BIM-EPIC locates the

pool in the JCL EXTENT statement.

 If the dataset is non-generation, BIM-EPIC deletes the old

version from the VTOC. For cataloged datasets, a new version is

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