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MVS Basics
1. INTRODUCTION TO IBM LARGE SYSTEMS................................................................................................3
Topics in this session.................................................................... ................................................................. .......3
Session Goals: .................................................................. .................................................................. .................. 3
I NTERNATIONAL BUSINESS MACHINES - A N OVERVIEW ...........................................................................................3IBM SOFTWARE PRODUCTS ......................................................................................................................................4
Small Systems ..................................................................... ................................................................ .................. 4
Workstations.........................................................................................................................................................4
Departmental Machines ...................................................................................................................... ................. 4
Large Systems....................... ..................................................................... ........................................................... 5
IBM LARGE SYSTEMS ...............................................................................................................................................5Typical Configurations.........................................................................................................................................5
IBM LARGE SYSTEMS - PROCESSORS........................................................................................................................7IBM LARGE SYSTEMS - DASD AND CONTROLLERS ..................................................................................................8IBM LARGE SYSTEMS - OFFLINE MEDIA DEVICES ....................................................................................................8IBM LARGE SYSTEMS - OTHER HARDWARE .............................................................................................................9IBM LARGE SYSTEMS - SOFTWARE OVERVIEW ......................................................................................................10
From a user's point of view... .............................................................................................................................10
THE EVOLUTION OF MVS/ESA .................................................................... ........................................................... 10DISCUSSION TOPICS - SESSION 1..............................................................................................................................11
2. CONCEPTS ............................................................... ................................................................... ........................ 12
Topics in this session..................................................................... ................................................................ .....12
Session Goals: .................................................................. .................................................................. ................12
INTRODUCTION TO OPERATING SYSTEMS.................................................................................................12
THE VON NEUMANN COMPUTING MODEL ................................................................................................................12THE ROLE OF AN OPERATING SYSTEM.....................................................................................................................13PROCESSOR MANAGEMENT.....................................................................................................................................13
The problem: ......................................................................................................................................................13
MEMORY MANAGEMENT ........................................................................................................................................13The problem: ......................................................................................................................................................13
Options:..............................................................................................................................................................13
Real memory implementations: ................................................................... ....................................................... 14
Virtual memory implementations: ............................................................ .......................................................... 14
I NPUT-OUTPUT MANAGEMENT ...............................................................................................................................14The problem: ......................................................................................................................................................14
A solution: ............................................................................................... ........................................................... 14
SPOOLING................................................................................................................................................................15 A special I/O problem: .............................................................................................................. ......................... 15
A solution: ............................................................................................... ........................................................... 15
I NFORMATION MANAGEMENT .................................................................................................................................15The problem: ......................................................................................................................................................15
Solutions:............................................................................................................................................................16
I NTERFACE TO USERS AND APPLICATIONS ..............................................................................................................16
THE MVS OPERATING SYSTEM .............................................................. ......................................................... 17
JOBS AND JOBSTEPS.................................................................................................................................................17ADDRESS SPACES ....................................................................................................................................................18THE CHANNEL SUBSYSTEM.....................................................................................................................................18SPOOLING................................................................................................................................................................19
THE STORAGE MANAGEMENT SUBSYSTEM .............................................................................................................19TSO, JES2, SYSTEM UTILITIES AND MACROS ..........................................................................................................20
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DISCUSSION TOPICS - SESSION 2..............................................................................................................................21
3. DATA MANAGEMENT......................................................................................................................................22
Topics in this session..................................................................... ................................................................ .....22
DATASETS ...............................................................................................................................................................22DATASET NAMES ....................................................................................................................................................22
DATASET ACCESS ...................................................................................................................................................23DATASET ORGANIZATION .......................................................................................................................................23ALLOCATING A DATASET ........................................................................................................................................24OFFLINE MAGNETIC MEDIA ....................................................................................................................................26ACCESSING DATA ....................................................................................................................................................27EFFICIENCY CONSIDERATIONS.................................................................................................................................28DISCUSSION TOPICS - SESSION 3..............................................................................................................................28
4. WORKING ON MVS AND USEFUL TIPS.......................................................................................................29
Topics in this session..................................................................... ................................................................ .....29
A USER PERSPECTIVE OF MVS .......................................................... ............................................................... .......29USEFUL TIPS ...........................................................................................................................................................30COMMON ABEND CODES.........................................................................................................................................30
SHARING DATASETS................................................................................................................................................31BATCH VERSUS O NLINE..........................................................................................................................................31USING SDSF ....................................................... ................................................................ .................................... 32WATCH YOUR DATASETS .......................................................................................................................................32LEARN I NSTALLATION CONVENTIONS.....................................................................................................................32HELP AND MANUALS ..............................................................................................................................................32
5. GLOSSARY..........................................................................................................................................................33
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1. Introduction to IBM Large Systems
Topics in this session
• IBM - the company
• IBM Large Systems
Session Goals:
• Historical Perspective
• Familiarity with Large Systems terminology
International Business Machines - An Overview
• Founded in 1913 in Endicott, New York as CTR (Computing,
Tabulating,Recording )• Became IBM in 1924
• The Watsons (TJ Sr(1914- 1956) , TJ Jr(1956-1974) ) were key figures in IBMtill the 70's
• Status as of early 1995:
• Headquartered at Armonk, New York
• World's largest IT company (1996 sales over US$ 72 billion)
• Chairman: Louis V. Gerstner
• Worldwide presence
• Significant investor in Research and Development
• Has a stake in all aspects of IT:
• Desk tops (The PC family. Intel, PowerPC based)
• Workstations (RS/6000 family)
• Departmental machines (The AS/400 family)
• Large Systems (ES/9000 family, ES/3090 family, 9672 R models, SP2
family)• Peripherals (Printers, disks, magnetic and optical devices,displays)
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• Semiconductor devices (processors, memory, other chips)
• Networking products (controllers, routers, bridgers, adapters)
• Services (Education, systems integration, consulting)
• Software
In the top 5 in most of these areas
IBM Software Products
Small SystemsOperating Systems (PC DOS, OS/2, AIX for PCs)
Language compilers (C Set, C Set ++, APL2, PL/I, REXX)Development tools (Visual Age, Visual Gen)Database and Transaction Management (DB2/2, CICS/2, IMS CS/2) Network software (LAN manager, LAN Netview)
WorkstationsOperating Systems (AIX/6000)Language compilers (C Set, C Set ++, XL Fortran/6000)Development tools (CMVC, Powerbench)
Database and Transaction Management (DB2/6000, CICS/6000) Network software (AIX SNA Server / 6000, AIX Lan ManagementUtilities/6000)
Departmental MachinesOperating Systems (OS/400)Language compilers (COBOL. REXX, RPG, C SET++, IntegratedLanguage Environment)
Development tools (VRPG, Client Series Application Development Toolset)Database and Transaction Management (DB2/400, CICS/400) Network software (LAN Server/400, Client Access/400, LANRES/400)
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Large SystemsOperating Systems (MVS/ESA, VM/ESA, VSE/ESA, TPF)
Language compilers (VS COBOL/II, COBOL/370, PL/I, C/370, REXX,VS/FORTRAN)Development tools (ISPF, CSP, CODE/370)Database and Transaction Management (DB2, IMS/ESA DM,CICS/ESA,IMS/ESA TM) Network software (VTAM, NCP. RSCS, NPSI, Netview)
IBM Large Systems
• Based on S/390 architecture (preceded by S/360, S/370, S/370-XA,ESA/370)• Wide range of hardware platforms
ES/9000 family (9221, 9121, 9021)9672 R modelsOlder machines (ES/3090, ES/4381, 30XX, 43XX. 370, 360)Plug Compatible Manufacturers (Amdahl, Fujitsu, Hitachi)
• Wide range of software
IBM softwareVendor software (Computer Associates, Legent, Compuware, CandleCorporation, SAP..)
• StrengthsReliabilitySecurityLarge capacity
Typical Configurations
Large databases, transaction processing environments
MVS/ESA, DB2, CICSMVS/ESA, IMS/ESA DB, CICSMVS/ESA, IMS/ESA DB, IMS/ESA TM
MVS/ESA, DB2, IMS/ESA TM
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IBM Large Systems - Processors
9221 family
Models like 110, 112, 114, 120, 130, 150, 170, 191, 200, 201, 211,221, 421Air cooled, rack mounted1 to 2 processors16MB to 512 MB central storage0 MB to 496 MB expanded storage8 to 24 channelsTCM based or CMOS based technology
9121 family
Models like 190, 210, 260, 311, 320, 411, 440, 480, 490, 511,521, 522, 570, 610, 622,732, 742Air cooled, frame mounted1 to 4 processors16MB to 512 MB central storage0 MB to 2048 MB expanded storage8 to 96 channelsTCM based technology
9021 family
Models like 330, 340, 500, 520, 580, 620, 640, 660, 711, 720, 742,820, 860, 900,932, 942, 952, 962, 972, 982, 9X2Water cooled, frame mounted1 to 10 processorsUpto 2 GB central storageUpto 8 GB expanded storageUpto 256 channelsTCM based technology
9672-R family
Three generations, 4 sub-families (Rx1, (Rx2,Rx3), Rx4)Models like R11, R21, R31, R41, R51, R61, RA2, R12, R22, R32, R42,R52, R62, R53, R63, RX3, RA4, RB4, R14, R24, R34, R44, RX4, RY4Air cooled, rack mounted1 to 10 processorsUpto 2 GB central storageUpto 48 channelsCMOS based technology
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IBM Large Systems - DASD and controllers
DASD (Count-Key-Data (CKD) ) devices
3380 family (eg. models D, J, K), with 47476 bytes per track, 615 MB to1845 MB per volume3390 family (eg. models 1, 2, 3, 9), with 56664 bytes per track, 924 MB to8315 MB per volumeVendor products emulating one of the above (StorageTek, Hitachi,EMC2)
DASD Controllers
3880 family3990 familyVendor products (Hitachi, EMC2)
IBM Large Systems - Offline Media devices
Cartridge devices
3480 family (18 tracks, 38 Kbpi, approx 210 MB per volume)3490 family (18 or 36 tracks, 38 Kbpi or 76 Kbpi, 210MB or 420 MB pervolume)Improved Data Recording Capability (IDRC) available for bothdevices, to almost double the data storageAutomated Cartridge Loader (ACL) available for both devices1995 announcement: Magstar drives, upto 10 GB per volume.
Automated Tape Libraries (ATL)
3495 system from IBM (Linear Array, robot on rails) Nearline system from StorageTek (Hexagonal configuration, central robotarm)
Optical Storage Devices
3995 system from IBM
Software support via Object Access Method (OAM)
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IBM Large Systems - Other Hardware
Printers
Line printers (1403 class, like 4245, 6262)Page printers (3800 class, like 3803, 3812, 3820, 3825)
Terminals
3270 family (3277, 3278, 3278-2, 3278-5, 3279, 3279-G)
Emulators (PC/3270, OS/2 communications manager)Vendor products for both the above
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IBM Large Systems - Software Overview
From a user's point of view...
TSO/E You log on to this and do interactive computingISPF You use this as a panel driven interface for TSO/EJCL You create batch jobs using this languageDCF You do document processing with this productGDDM You do graphics processing with this productDB2 This is the relational DBMSIMS DB This is the hierarchical DBMS
CICS This is a Transaction Processing systemIMS TM This is another Transaction Processing systemCSP This is a 4 GL application development / execution environmentRACF This product manages access securityVTAM This product controls all networkingJES2 This component of MVS/ESA manages all foreground and batchtasksDFSMS This component of MVS/ESA manages all dataREXX This is a powerful shell programming language
The evolution of MVS/ESA
Year Event
1964 System 360 announced1965 Basic Operating System (BOS)1966 Primary Control Program (PCP), Multiprogramming with Fixed
number of Tasks (OS/MFT), Multiprogramming with Variablenumber of Tasks (OS/MVT)1966-70 Houston Automatic Spooling Program (HASP), Time Sharing Option
(TSO),Telecommunications Access Method (TCAM),Customer InformationControlSystem (CICS), Information Management System (IMS)
1970 System 370 announced1972 Operating System / Virtual Storage 1 and 2 (OS/VS1, OS/VS2)1974 Multiple Virtual Storage (MVS)
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1974-80 Job Entry Subsystems 2 and 3 (JES2, JES3), Resource Access ControlFacility (RACF),
Virtual Telecommunication Access Method(VTAM)1981 System 370 Extended Architecture (370-XA) and MVS/XA
announced1983 Database 2 (DB2) announced1988 Enterprise Systems / 370 Architecture (ESA/370), MVS/ESA
announced1990 System 390 announced1993 MVS Open Edition (POSIX features)1995 MVS/ESA 5.2.2 with full POSIX, XPG4, X/OPEN1996 OS/390 Release 1 - Open Server for Network computing .1997 OS/390 Release 3 compliance - an integrated enterprise server
operating system.Uniqule suited to integrate today’s heterogeneous and multi-vendorenvironment.
Discussion topics - Session 1
What are the first words that come to your mind when someone says,'IBM Mainframes'?Where do you think IBM Large Systems are headed?Who do you think are the Large systems users today?
End of Session 1
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2. Concepts
Topics in this session
• Introduction to Operating Systems
• The MVS/ESA Operating System
Session Goals:
• Introduce basic Operating System concepts
• Introduce MVS/ESA
Introduction to Operating Systems
We will talk about:
• The von Neumann computing model
• The role of an Operating System
• Processor Management• Memory Management
• Input/Output Management
• Spooling
• Information Management
The von Neumann computing model
• Most common model for computing systems• Proposed by John von Neumann in the 1940's
• Defines a computing system in terms of elements:
ProcessorMemoryControl element
• A program (code and data) must be placed in memory by the control element
• After this, the processor executes the program one instruction at a time
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The role of an Operating System
Manage hardware resources in the computing system:• Processor
• Memory
• Input/Output
• Printers
• InformationProvide services to application programs and end-users through well definedinterfacesDo all this, as efficiently as possible
Processor Management
The problem:
• The computing model says that at any instant, only one task can beexecuting on a given processor (the 'active' task)
• What if the task is waiting for a time-consuming operation, say an I/O?
• Processors are expensive, must be utilized as fully as possible
A solution
• Offload I/O to dedicated I/O processors
• Have a large number of tasks in a 'ready to run' state
• Other tasks are in 'wait' states, possibly doing I/O
• Net result: The operating system has a wide range of options inchoosing the next task to execute
• Price: Increased complexity
Memory Management
The problem:All code and data for a given task must be in memory for a task to be executable
Options:
• Place tasks in 'real' memory
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• Place tasks in 'virtual' memory
Real memory implementations:
• Code and data are in real memory• Size of code and data limited by size of installed memory
• Good performance, low overhead
• Possible wastage of memory
Virtual memory implementations:
• Based on the assumption that for a given task, not all code and data needto be in real memory all the time
• Implemented as a combination of real and auxiliary (disk) storage
• The operating system takes the responsibility of bringing in the required parts of a task into real memory, when required
• The task is completely unaware of this, and sees only virtual memory.
• It may of course experience delays
• Advantage: Code and data size now independent of real memory
• Disadvantage: Increased overhead, poorer performance
Input-Output Management
The problem:
• Applications should not worry about device characteristics
• I/O device speeds are typically 1000 times slower than processors• Processors too powerful and expensive to waste on I/O
A solution:
Let all I/O be handled by a specialized system (The I/O subsystem)
The I/O subsystem:
• Consists of I/O processors, device controllers and devices• Receives an I/O request in a standard format
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• Handles all interactions with the actual devices
• Moves data between memory and the device and vice-versa
• Notifies the processor at the end of the operation
While the I/O subsystem is processing the request, the processor is free to executeother work
Spooling
A special I/O problem:
• Some devices (like printers) can handle only one job at a time
• Requests for such 'unit record' devices must be serialised
A solution:
• 'Spooling' (Simultaneous Peripheral Operation On Line)
• All output to spooled devices is first written to disk
• The spool manager then provides facilities like:
Release output to actual printersSelective delete processingError handlingRecovery and restart
Information Management
The problem:
• The application is interested in information, not data
• Organising and presenting data in a useful form
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Solutions:
• Files and File systems
• Access methods or device drivers
• System Managed Storage
Interface to Users and Applications
User interface is of several kinds:
• Online user interface
• Batch user interface
• Application programming interface
Online user interface:
• is the 'face' of the operating system
• is where small systems are far ahead of large systems
Batch user interface:
• May allow batch and online to interact
• Is often the 'workhorse' of large systems
Application programming interface
• Usually by means of callable services
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The MVS Operating System
Let's apply the same concepts to MVS...
Processor Management: Jobs and JobstepsMemory Management: Address SpacesI/O Management: Channel SubsystemSpooling: Job Entry SubsystemInformation Management: Storage Management SubsystemUser interface: TSO, JES2, system utilities and macros
Jobs and Jobsteps
"JOB" in MVS is a generic term for any work to be performed
A Job could be:
• An online user
• A system task• A subsystem
• A 'real' batch job
A Jobstep is the execution of a single program within a job
A job consists of one or more jobsteps
Examples of jobsteps:
• The terminal monitor program for an online user
• A control program for a system task or subsystem
• A user program or system utility
A jobstep (task) could create several sub-tasks. It is then responsible for managingall these sub-tasksThe Job Entry Subsystem manages all jobs and jobsteps
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Address Spaces
• An address space is the amount of virtual storage seen by a job
MB in MVS/SP and older systemsGB in MVS/XA and MVS/ESA
• Each job executes in an address space
• Online users each have a Time Sharing User (TSU) address space
• Batch jobs execute in an Initiator address space
• An address space is organized as a set of:
Segments (1MB each)Pages (256 pages per segment, each page is 4K)
• An address space is either:
Swapped out (all segments are on auxiliary storage)Swapped in (at least one segment is in real storage)
• An address space:
• Contains read-only copies of operating system areas
• Competes with other address spaces for resources
• Is normally isolated from other address spaces
• MVS/ESA provides data spaces and hiperspaces for additional, data-only use
by applications
The Channel Subsystem
Handles all Input/OutputAn application needing to perform I/O, can:
• Interface directly with the channel subsystem (channel programming)
• Use standard operating system routines (access methods)
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In either case, the channel subsystem:
• Receives I/O instructions
• Receives an associated set of commands (the channel program)• Communicates the request to the appropriate device
• Moves data from the devices to memory or vice-versa
• Signals completion of the operation
An access method is preferred because:
• The application is shielded from device details
• A standard interface is provided by MVS
Spooling
• Managed by the Job Entry Subsystem (JES)
• All outputs intended for printing are first stored in special, 'spool' DASD
• Can be viewed and manipulated from an online session usingthe System Display and Search Facility (SDSF)
• Outputs are normally in the 'Held' queue, unless released to the 'Output'
queue• JES also uses the spool for managing batch queues
The Storage Management Subsystem
• Creates and manages the MVS 'file system'
• All information is in the form of 'datasets'.
• Information about datasets is in Catalogs, VTOCs and Volume labels
• Datasets allow various modes of access and organization:
1. Sequential2. Random
3. Direct
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• SMS allows actions on datasets like:
Allocate
DeleteBackupMigrateRecall
The MVS 'file system' was largely non-hierarchical till recentlyThe new MVS provides a POSIX compliant file system in addition to thetraditional file system
TSO, JES2, System util it ies and macros
• The MVS online interface is usually via TSO
TSO is line mode, command drivenISPF is used to provide a screen based, menu driven front-end
• JES2 manages all batch work
TSO users can submit jobs to batch via TSO SUBMIT commandCan use SDSF to view and manipulate batch
• Application programming interface
System utilities and services availableAssembler interface necessary for most services
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Discussion topics - Session 2
.What are the fundamental differences in the design philosophy of a single useroperating system like MS-DOS and a complex operating system like MVS/ESA?
MVS/SP provided a 16 MB address space with 24 address bits. MVS/XAand MVS/ESA provide a 2 GB address space with 31 address bits. Whatcompatibility issues would you consider, to execute MVS/SP code onMVS/ESA?
Hint: Think of the addressing mode (AMODE), and the residence mode(RMODE).
End of Session 2
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3. Data Management
Topics in this session• Datasets and Catalogs
• System Managed Storage
• Offline Magnetic Media
• Accessing and using data
• Efficiency considerations
Session Goals: • How to define and use data on MVS
Datasets
• Named collection of data
• Resides on peripherals like DASD, tape
• Treated as a single entity by the operating system and applications
• Typical operations on a dataset include:
AllocateWriteReadUpdateCopyBackup / ArchiveDeleteRestore
Migrate / Recall
Dataset Names
• A qualifier:
• Is 1 to 8 characters long
• Begins with an alphabet (A-Z)
• Consists of Alphabets (A-Z), Numerals (0-9), National Characters(#, @,$)
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• Looks like: ABDCE, B1290, DT951010
• A dataset name:
• Consists of one or more qualifiers• Each qualifier is separated from the other by a period '.'
• Is 1 to 44 characters long for DASD datasets
• Is 1 to 17 characters long for tape datasets
• Looks like: SYS2.USER.DOC, USERID.BACKUP.DT181095, A,A.A.A.A.A.A
The first qualifier is called the High Level Qualifier (HLQ) Note: No hierarchy is implied by the qualifiers
Dataset Access
• To be easily accessible, a dataset must be retrievable by name
• Two modes of retrieval allowed:
By name, if names are uniqueBy name and volume name, if names are not unique
• This implies two levels of location information:
Global (in Catalogs)Local (using the Volume Table of Contents or VTOCs, or tape labels)
• Catalogs form a tree structure
• HLQs form the basis of the pointers from the root ('Master Catalog') to theleaves ('User Catalogs')
Dataset Organization
• Physical Sequential (PS)
Records stored in time order of writingAccess is sequentialCan reside on DASD and tape (tape datasets are always PS)
Located by name: eg., BTPROJ.SEQ.DATASET
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• Partitioned (PDS or PO)
Collection of one or more PS datasets ('members'), related by a directoryOne level hierarchy - all members have the same characteristics
The PDS name alone is stored in the Catalog / VTOCMember names and location information in the directoryA member name follows the same rules as a qualifierCan reside only on DASDLocated by name + member name: XYPROJ.USERID.NOTES(N1234567)
• Partitioned - Extended (PDSE)
PDS-like in organization
Eliminates several problems associated with PDSsAvailable only in later MVS versions (post-1989)Must always be cataloged, SMS managed
• Virtual Storage Access Method (VSAM)
Entry Sequenced (ESDS)Key Sequenced (KSDS)Relative Record (RRDS)Linear (LDS)Variable length Relative record (VRRDS)
• Others
Direct (DA)Indexed Sequential (IS)
Allocating a dataset570275
• Datasets need to be pre-allocated before use
• Allocation can use installation defined defaults
• Parameters for allocation:
NameLocationSize
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Attributes
• Name: As described earlier
• Location:
Could be a volume name + unit type - Eg,VOL=SER=CART01,UNIT=CARTCould be a SMS storage class name - Eg, STORCLAS=DEVSCCould use system default location
• Size, in blocks, tracks or cylinders
Primary allocation
Secondary allocation Number of directory blocks (for PDSs)
• Attributes
Block size -how many records in one IO?Record length -howmany byte in a record?Record format -Fixed,Variable,Undefined?SMS Management Class name
SMS Data Class name
Examples:
DD DSN=USERID.TEMP,SPACE=(CYL,(1,1))
Note: Uses system defaults
DD DSN=USERID.TEMP,DISP=(NEW,CATLG),SPACE=(CYL,(1,1)),STORCLAS=DEVSC,DATACLAS=PS,MGMTCLAS=STANDMC
Note: Uses SMS constructs
DD DSN=USERID.TEMP,DISP=(NEW,CATLG),SPACE=(CYL,(1,1)),UNIT=DISK,VOL=SER=WORK01,DCB=(DSORG=PS,LRECL=80,BLKSIZE=9040,RECFM=FB)
Note: Specifies all details
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System Managed Storage
• Older MVS systems expect the user and the storage administrator to managedata manually
• System Managed Storage provides:
Policy based storage administrationDevice independent dataset usageAutomated data management
• SMS managed datasets must:
be catalogedreside on a SMS managed volumehave SMS constructs like storage class, data class, management classand storage group associated with them
• New functionality offered only for SMS managed data. Eg.,
PDSEData compression
Offline Magnetic Media
• Tape and Cartridge datasets
• Several recording modes and geometries:
7 or 9 track tapes18, 36 track cartridges128 track cartridges (Magstar only)
• Data compression options:
No compression on tapesImproved Data Recording Capability (IDRC) for 18, 36 track cartridge
• Files and Volumes can have the following relationships:
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Multiple files on a single volumeSingle file on multiple volumesAny combination of the above
• Files on a tape are separated by a special pattern called a Tape Mark• Two tape marks without intervening data signal end of volume
• Labels (which are system generated files) are used to provide user data filedescriptions
Standard labels (SL)User defined labels (UL) No labels (NL)ANSI standard labels (AL)
Accessing data
• Some standard access methods:
Basic Sequential Access Method (BSAM)Queued Sequential Access Method (QSAM)Basic Partitioned Access Method (BPAM)
Virtual Storage Access Method (VSAM)
• Access methods:
are invoked through a standard interface build actual channel programsinteract with the input/output supervisor
• Advantages to the user:
Shielded from device detailsCan use standard interface from low and high level languagesPortable code
Assembler language interface provides greater control over the access methodChannel programming also possible from assembler
Note: High level languages provide the familiar verbs (OPEN, CLOSE, READ,WRITE).
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Efficiency considerations
• Block sizes
Small block sizes cause additional I/OBad block sizes waste spaceGood blocking for DASD: 1/2 track (eg, 23440 for 3380, 27920 for 3390)
• Multiple PS datasets versus PDS/PDSE members
A single PS cannot be smaller than 1 track - a PDS/PDSE membercan share tracks with other membersEach PS needs a Catalog and a VTOC entry - the entire PDS/PDSE has
one Catalog and 1 VTOC entryEach member of a PDS/PDSE must have the same characteristics like
record length
• Space parameters for allocation
Bad primary / secondary allocation parameters can cause unnecessaryfragmentation, 'out of space' errorsA PDS often runs of out space, needs to be 'compressed'
A PDS often runs out of directory space
Discussion topics - Session 3
How would system managed storage help in a non-MVS environment?
When would you code assembler routines for I/O?How can you have duplicate datasets names in MVS?
End of Session 3
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To create your own executable code, you normally would:
• Allocate required datasets (source, object, load libraries)
• Write the code using an editor (usually ISPF)• Compile the code into a text deck and store in an object library
• Execute the text deck using the LOADER, or
• Create a load module using the LINKER or an executable object usingthe BINDER
• A load module or an executable object can be executed independently ina jobstep
Many system utilities are available in the global environment for foreground and
batch, like:CompilersLoader / Linker / BinderCopyBackupSort
Useful Tips• Common Abend Codes• Sharing datasets
• SDSF Usage
• Batch Versus Online
• Watch your datasets
• Learn Installation Conventions
• Help and Manuals
Common Abend Codes
An Abend is an Abnormal End of a program. Abend codes point todiagnostic information. Common codes are:
S0C1 Operation Exception. For example, dataset Open errorS0C4 Protection Exception. For example, invalid pointer valueS0C7 Data Exception. For example, Alphabet used in arithmeticS0C9 Fixed Point overflow. For example, divide by Zero
S222 Job cancelled
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S322 Job exceeds time limit for specified classS806 Load module not foundS813 Datasetname mismatch on tape labelS913 Security violation
S878 Insufficient virtual storageSx37 Series of DASD space related conditions
Sharing Datasets
MVS recognizes two types of access:
• Exclusive access (DISP=OLD or MOD)
• Shared access (DISP=SHR)
Data integrity not guaranteed for shared access, unless provided by subsystem or application
Don't compress a PDS being written by another user...
Batch Versus Online
Online interactions are biased towards short transactions. Batch is biased for longrunning transactions. Use online for:
• Interactive work like editing, data entry
• Debugging
• Documentation
Use batch for:
• Compiles
• Test execution
• Backups / restores
• Any long running operation eg, sort, copy
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Using SDSF
• Don't watch your batch job in real time• Hitting ENTER on the active queue list in SDSF actually makes your job run
slower
Watch Your Datasets
• Each dataset is accessed by a program via a DD name
• Make sure the DD name points to the dataset you want• Most common errors:
Linkage editor output DD (SYSLMOD) points to the source code datasetSource and Target of copy get exchanged
Learn Installation Conventions
• Every installation has its own conventions
• Ask for or locate the NEWS or BULLETIN BOARD
• Follow installation standards
Help and Manuals
TSO/E and ISPF come with online helpBookManager and equivalent products provide softcopy of manualsHardcopy manuals availableEvery error condition is accompanied by a messageMessages manuals provide additional informationEach message has an explanation and suggested actionsSuggested manuals:
User Guides and reference for TSO, ISPF, JCL, REXX, COBOL...Utilities manualDFSORT user guide, reference
Linkage Editor and Binder User Guide, reference
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5. GLOSSARY
Abend Abnormal EndBLKSIZE Block SizeBOS Basic Operating SystemBPAM Basic Partitioned Access MethodBSAM Basic Sequential Access MethodCICS Customer Information Control SystemCKD Count-Key-Data (type of DASD)CMOS Complementary Metal Oxide SemiconductorCMS Conversational Monitor System (part of VM)CMVC Configuration Management and Version ControlCSP Cross System ProductDA Direct Access (type of dataset organization)DASD Direct Access Storage DeviceDATACLAS SMS data class parameter in JCL and TSODataspaces Data-only virtual memory available to a task, byte addressible, (2GB)DBMS Database Management SystemDCB Dataset Control BlockDCF Document Composition FacilityDD Data Definition (type of statement in JCL)
DFSMS Data Facility Storage Management SubsystemDISP Disposition (parameter in JCL)DSORG Dataset Organization (parameter in JCL)ES Enterprise SystemsESA Enterprise Systems ArchitectureESDS Entry Sequenced Dataset (type of VSAM dataset)FBA Fixed Block Architecture (type of DASD)GB Gigabytes (2 ** 9 bytes)GDDM Graphical Data Display Manager
Hiperspaces High Performance data spaces, page addressibleHASP Houston Automatic Spooling ProgramHLQ High Level QualifierIBM International Business MachinesIDRC Improved Data Recording CapabilityIMS Information Management SystemIMS/ESA DM IMS database managerIMS/ESA TM IMS transaction managerISPF Interactive System Productivity Facility
JCL Job Control LanguageJES Job Entry Subsystem
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Kbpi Kilobytes per inchKSDS Key Sequenced Dataset (type of VSAM dataset)LANRES LAN Resource ExtensionsLDS Linear dataset (type of VSAM dataset)
LRECL Logical Record Length (TSO, JCL parameter)Magstar 3580 cartridge system from IBMMB MegabytesMVS Multiple Virtual StorageMVS/ESA MVS / Enterprise Systems ArchitectureMVS/SP MVS / System ProductMVS/XA MVS / Extended Architecture
Netview Network Management product from IBM NCP Network Control Program NL No Label NPSI Network Packet Switched InterfaceOAM Object Access MethodOS/MFT Operating System / Multiprogramming with Fixed number of TasksOS/MVT Operating System / Multiprogramming with Variable number of tasksOS/390 Operating System / 390, the new name for MVS, after MVS/ESA
5.2.2PowerPC Performance Optimization With Enhanced Risc - Performance ChipPCP Primary Control Program
PDS Partitioned datasetPDSE Partitioned dataset - ExtendedPL/I Programming Language / 1PM Presentation ManagerPOSIX Portable Operating System Standard from IEEEPR/SM Processor Resource / System ManagerPROC Procedure (JCL parameter)PS Physical SequentialQSAM Queued Sequential Access Method
RACF Resource Access Control FacilityRAMAC 9394 / 9395 DASD system from IBMREXX Restructured Extended ExecutorRMODE Residence ModeRRDS Relative Record Dataset (VSAm dataset type)_RS RISC SystemRSCS Remote Spooling and Communication SubsystemSAP Package from SAP AGSDSF System Display Search Facility
SL Standard Label (JCL parameter)SMS System Managed Storage
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STORCLAS JCL / TSO parameter for SMS storageclassTCAM Telecommunication Access MethodTCM Thermal Conduction ModuleTMP Terminal Monitor Program
TPF Transaction Processing FacilityTSO/E Time Sharing Option / ExtensionsTSU Time Sharing UserUL User defined label (JCL parameter)VM/ESA Virtual Machine / Enterprise Systems ArchitectureVOLSER Volume Serial (JCL parameter)VRPG Visual RPGVRRDS Variable length Relative Record Dataset (VSAM dataset type)VSAM Virtual Storage Access MethodVSE/ESA Virtual Storage Extended / Enterprise Systems ArchitectureVTAM Virtual Telecommunications Access MethodVTOC Volume Table of ContentsWAN Wide Area Network