Chapter 6: Accessing large amount of data

Introduction to the new mainframe:Large-Scale Commercial Computing

© Copyright IBM Corp., 2006. All rights reserved.

Chapter 6: Accessing large amount of data

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Introduction to the new mainframe


Chapter objectives

After completing this chapter, you should be able to describe the concepts of:• Channel subsystems• Control Units• DASD• RAID• Multiple allegiance/ PAV• Random access to data• Databases• Data sharing• DFSMS

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Introduction

The core function of a large-scale computing environment is to process corporate data.

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I/O Connectivity

CHANNEL SUBSYSTEM

CONTROLUNIT

PRINTER DASD

CONTROLUNIT

CPU CPU

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Channel Subsystem

Storage

CPU CPU

SAPSAP

Channel SubsystemEscon and Ficon

CU

CU CU

CUSwitch Switch

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Control units

To execute channel commandsProtocol : CCWChain : an operation that consist of more than 1

CCWAllow functionality beyond the power of the early

mainframe processors

Beginning : 1 device to 1 control unitNow : 1 device can connect to > 1 control unit

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Direct Access Storage Device (DASD) Architecture

head headheadhead data datadata

Gap, Sync

startsector

startsector

startsector

startsector

sector i-1 sector i sector i+1

Fixed Block Record Format

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DASD Architecture (Cont...)

Count, Key, Data (CKD) Format

Gap, Sync

countkeycountkeycount data datadata key

record i-1 record i record i+1startrecord

startrecord

startrecord

startrecord

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Mapping for access to devices

UCB Unit Control Block

UCW Unit Control Word

CUCB Control unit control block

The CSS uses the UCW to find the CUCBs and decides The CSS uses the UCW to find the CUCBs and decides which is the best channel/control unit pair to use for the which is the best channel/control unit pair to use for the operation.operation.

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Mapping for access to devices (Cont...)

z/OSUCB

CUESCDESCD

Unitaddress '0A'

Device number

200A

ESCON/FICONI/O interface

Unit adress

UA=0A

1A

2A

8A

9A

ESCDESCD

ESCDESCD

ESCDESCD

CHANNELSUBSYSTEM

UCW

CU

CU

CU

subchannelnumber

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DASD Subsystem

FF00

FF01

FF02

FF03

20002001200220032004

200520062007

20082009

200A200B200C

200D200E

200F

CU

CU

disk drives

ESCON/FICON Directors

A control unit may be connected to several channels, and a device may be connected to several control units. This capability is a reason for operational availibility and resilience. Between the control unit and the IBM System z an ESCON or FICON-Director can be connected in addition. That will increase the systems stability and scalability.

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Redundant array of independent disk (RAID)

data 1data 2data 3data 4data 5data 6data 7data 8

data 1

data 5

data 2

data 3

data 4

data 6

data 7

data 8

RAID 5

party 4-7

party 3-6

party1-8

There is a variety of common and insignificant RAID-level. RAID-5 has a high I/O rate and a medium data rate. RAID-5 is used by the IBM DS8000 controller arrays in the majority of configurations.

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Reducing the number of logical volumes

Amount of Data

problem : to manage logical volumes

solution : DFSMS

Larger Volumes

problem : more I/O to each volume

solution : RAID

BUT... Is not enough...

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Multiple allegiance(MA)/Parallel access volume(PAV)

MA PAV

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Random access to data

RAID : First slow, as of next high-speed retrieval

Predictive loading : load the data into the CONTROL UNIT CACHE

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Databases

likely on relational databases

a single large server controlling all data request

not on mainframe (clients & server on different machine):

• Good data integrity

• Poor processor utilization

on mainframe (clients & server on same machine) :

• Good data integrity

• Good processor utilization

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Data Sharing

The ability to share data for both reading and updating, from multiple programs that can be running on different physical machines.

Parallel Sysplex is required

with structures in the Coupling Facility (CF) providing the necessary mechanisms

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Data facility Storage Management System

Object Access Method (OAM) Tape library OAM uses a hierarchy:

• DASD• Tape volumes with a tape library device• Optical volumes inside a library device

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Data placement and management

Performance

Space

Backup

Migration

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Summary

The New Mainframe and access large amounts of data:• Access large amounts data is required for a variety of

applications• Requires a high processor utilization• High levels of reliability are needed• Tape media : high capacity, low cost, but slow and sequential• Quick data transfer rates are need

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Key terms in this chapter

• Channel subsystem• CKD• Control block• Control Unit• DASD• Data Sharing

• DFSMS• FBA• Logical address• PAV• RAID

Chapter 6: Accessing large amount of data

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