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BIM-EPIC System Datasets Introduction

Chapter 2. Installing the Basic System 2-17

BIM-EPIC System Datasets

Introduction

Because BIM-EPIC's System Datasets are proprietary, physically chained

databases, the following two conditions must be met for safe caching:

• The caching device must be one of the following:

• WRITE-THROUGH where writes are committed to disk before the device/channel

end is provided. Another term sometimes used is READ-ONLY CACHE, meaning

that only reads are cached.

•

100% NON-VOLATILE, so that the device will never fail (e.g., devices with internal

UPS). If this is the case, the device must also handle failed writes dynamically. If

the device fails or write requests cannot remain cached, forward recovery will not

properly recover the DSN Catalog.

• I/O must not be reordered to optimize performance, either by the caching controller, the

operating system, or a vendor product at the operating system level. The I/O must

be processed in the order in which it was presented by BIM-EPIC.

BIM-EPIC uses the DSN Catalog to maintain information about files under its control. Freed

records are automatically reused and the file structure is self-reorganizing.

The Recorder File logs changes to the DSN Catalog. The Recorder File serves as security

against data loss if the DSN Catalog is damaged. The Recorder File can also be used for

BIM-EPIC’s job accounting reports and displays. It should be dumped and cleared on a

regular basis.

BIM-EPIC uses the JOBQ to control job-specific functions such as:

• Purging datasets

• Controlling common workfiles

• Supporting BIM-EPIC DD statements

The JOBQ can reside within the DSN Catalog (it need not be a separate file), but system

performance can be enhanced by using a JOBQ that is a separate VSE file. If a separate

JOBQ is not defined, BIM-EPIC places the JOBQ in the DSN Catalog by default.

In single CPU environments, improved BIM-EPIC Performance is the only reason to create

the JOBQ as a separate file.

In multiple CPU environments (Real, LPAR, or VM Guests), if the BIM-EPIC Catalog is

shared, a separate JOBQ file MUST be used for each CPU.

Freed JOBQ records are automatically reused and the file structure is self-reorganizing.

BIM-EPIC System

Dataset Caching

DSN Catalog

Recorder File

JOBQ

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Memorex LOCK - VERSION 2-24 Especificaciones Pagina 45