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Disk Processing BIM-EPIC Job Control

1-42 User Reference

Disk Processing

The tasks required for disk open and end-of-extent processing are similar to those for tape.

BIM-EPIC reads the DSN Catalog, issues messages, makes an assignment, and so on. For

disk, however, BIM-EPIC must make the allocation, which is more complicated than finding

the correct tape volume.

At every open, VSE reads the VTOC sequentially, which can require thousands of I/O

operations. BIM-EPIC provides the Quick Disk Allocation System (QDAS) to dramatically

decrease the time required to allocate an output dataset.

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

when the system is initialized. When disk space is used or freed for any dataset (controlled or

uncontrolled), QDAS updates its map in storage.

Operational Notes: QDAS only updates its maps 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 its 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

the BIM-EPIC Installation and System Guide for procedures.

Because QDAS only maps free space, it is necessary to refresh its tables daily to pick up the

space made available by Start Track 1 files that have expired. This is not necessary if all your

disk files are catalog controlled. It is recommended that this procedure be performed daily

after midnight as part of the BIM-EPIC daily maintenance procedures. See “Regular

Maintenance” in Chapter 4 of the BIM-EPIC Installation and System Guide for further

information.

1. BIM-EPIC locates the pool to which the dataset is assigned. For cataloged datasets, it

finds the pool in the DSN Catalog entry. For Start Track 1 datasets, it finds the pool that is

specified in the JCL.

2. If the dataset is non-generation, BIM-EPIC deletes the old version. This is simple for

cataloged datasets, since the location of the dataset is contained in the DSN Catalog. For Start

Track 1 datasets, BIM-EPIC has to read each VTOC in the pool until it finds the old dataset.

3. BIM-EPIC decides which disk volume in that pool will be allocated using the leveling

feature, if active, so that datasets will be allocated evenly across all volumes in the pool.

4. BIM-EPIC checks the VTOC (or QDAS) for a large enough free extent. (BIM-EPIC does

not find free extents through the DSN Catalog.) If it cannot find sufficient space in the pool

for the extent, it issues a message and waits for a response from the operator.

5. BIM-EPIC updates the VSE Label Area, creating an extent and assigning the disk volume.

Open and End-of-

Extent Processing

Quick Disk

Allocation (QDAS)

On Output

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Memorex LOCK - VERSION 2-24 Especificaciones Pagina 56