Memorex LOCK - VERSION 2-24 Technical Information PDF herunterladen (Seite 63)

100

101

Using Disk Processing

User Reference

Use Pursuant to Company Instructions

1-45

created. in the DSN Catalog and on the VTOC. For Start Track 1

datasets, BIM-EPIC must read each VTOC in the pool until the

old dataset is located.

 BIM-EPIC decides which pool volume to allocate. BIM-EPIC

checks the VTOC or QDAS map for a free extent with sufficient

space. If BIM-EPIC cannot locate sufficient space in the pool for

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

operator.

 BIM-EPIC updates the VSE Label Area, creating an extent and

assigning the disk volume.

The following events occur on input.

 BIM-EPIC locates the dataset. For cataloged datasets, BIM-EPIC

locates the dataset’s location allocation in the DSN Catalog. For

Start Track 1 datasets, BIM-EPIC reads each VTOC in the pool

until it finds the first extent of the dataset. Depending on how

many VTOCs must be read, this process can involve a large

amount of I/O.

 BIM-EPIC updates the VSE Label Area, creating an extent and

assigning the disk volume.

It is strongly recommend that you use cataloged datasets instead of Start

Track 1 datasets. Cataloged dataset processing is more efficient than Start

Track 1 processing. Although BIM-EPIC must write to the DSN Catalog

each time it accesses a cataloged dataset, BIM-EPIC uses far fewer I/O

operations than would be required to read all the VTOC entries in the disk

pool. In general, if you want to use Start Track 1 datasets, consider doing

so only for disk pools that contain fewer than three volumes.

Space Holder

Records

Each time BIM-EPIC allocates an extent for a dataset, BIM-EPIC writes a

VTOC entry called a Space Holder record. Space Holder records prevent

the same space from being used when allocating another BIM-EPIC

dataset. The VTOC entry for a Space Holder record contains the name of

the dataset with a right parenthesis substituted for the first letter, for

example, )ATASET.NAME for DATASET.NAME. The entry is written

with the current date as the expiration date.

Close Processing provides additional detail on Space Holder record

usage.

Processing

When a program requests close processing for a dataset, some records

may remain in the buffer. These records are written to disk when VSE

closes the dataset. In some cases, there are too many records in the buffer

to fit in the space remaining in the current extent. When this occurs,

another extent is necessary to accommodate the excess records.

1 2 ... 58 59 60 61 62 63 64 65 66 67 68 ... 567 568

Kommentare zu diesen Handbüchern

Keine Kommentare

Memorex LOCK - VERSION 2-24 Technical Information Seite 63

Kommentare zu diesen Handbüchern