version 2 release 4 z/os - ibm · chapter 4. backing up and recovering data sets.....47 using repro...

z/OS: z/OS DFSMS Using Data SetsDFSMS Using Data Sets
IBM
SC23-6855-40
Note
Before using this information and the product it supports, read the information in “Notices” on page 585.
This edition applies to Version 2 Release 4 of z/OS (5650-ZOS) and to all subsequent releases and modifications until otherwise indicated in new editions.
Last updated: 2020-02-24 © Copyright International Business Machines Corporation 1987, 2020. US Government Users Restricted Rights – Use, duplication or disclosure restricted by GSA ADP Schedule Contract with IBM Corp.
Contents
Multivolume VSAM data sets..........................................................................................................39 Multivolume non-VSAM data sets.................................................................................................. 39 Extended-format data sets.............................................................................................................39
Extension to another DASD volume.....................................................................................................43 Multiple volume considerations for sequential data sets................................................................... 43 Extended address volumes..................................................................................................................44 Additional information on space allocation.........................................................................................46
Structure of an exported data set.................................................................................................. 49 EXPORT and IMPORT commands.................................................................................................. 49
Handling an abnormal termination................................................................................................ 51 Using VERIFY to process improperly closed data sets..................................................................51
Chapter 6. Organizing VSAM data sets......................................................................................................75 VSAM data formats...............................................................................................................................75
Naming a cluster...........................................................................................................................102 Specifying cluster information..................................................................................................... 103 Using access method services parameters................................................................................. 104 Allocating space for VSAM data sets............................................................................................106 Calculating space for the data component of a KSDS................................................................. 109 Calculating space for the index component................................................................................ 109 Using ALTER to modify attributes of a component......................................................................110 Using ALTER to rename data sets................................................................................................ 110
Copying and merging data sets......................................................................................................... 113 Defining alternate indexes................................................................................................................. 115
Examples of defining alternate indexes and paths........................................................................... 124 JCL statements............................................................................................................................. 124 Commands....................................................................................................................................124
Requesting access to a data set........................................................................................................ 132 Inserting and adding records....................................................................................................... 133 Retrieving records........................................................................................................................ 134 Updating records.......................................................................................................................... 136 Deleting records........................................................................................................................... 136 Deferring and forcing buffer writing.............................................................................................137 Retaining and positioning data buffers........................................................................................ 137 Processing multiple strings.......................................................................................................... 137 Making concurrent requests.........................................................................................................138 Using a path to access records.................................................................................................... 139 Making asynchronous requests....................................................................................................139 Ending a request...........................................................................................................................140
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Management of I/O Buffers for Shared Resources........................................................................... 195 Deferring Write Requests............................................................................................................. 195 Relating Deferred Requests by Transaction ID........................................................................... 196 Writing Buffers Whose Writing is Deferred: WRTBFR..................................................................196 Accessing a Control Interval with Shared Resources..................................................................197
Chapter 14. Using VSAM record-level sharing........................................................................................201 Controlling Access to VSAM Data Sets.............................................................................................. 201 Accessing data sets using DFSMStvs and VSAM record-level sharing.............................................201
Record-Level Sharing CF Caching................................................................................................ 202 VSAM Record-Level Sharing Multiple Lock Structure..................................................................203 Using VSAM RLS with CICS...........................................................................................................203 Non-CICS Use of VSAM RLS......................................................................................................... 205 Using 64-Bit Addressable Data Buffers....................................................................................... 206 Read Sharing of Recoverable Data Sets.......................................................................................207 Read-Sharing Integrity across KSDS CI and CA Splits................................................................ 207 Read and Write Sharing of Nonrecoverable Data Sets................................................................ 207 Using Non-RLS Access to VSAM Data Sets.................................................................................. 208 RLS Access Rules..........................................................................................................................208 Comparing RLS Access and Non-RLS Access.............................................................................. 209 Requesting VSAM RLS Run-Mode................................................................................................ 211 Using VSAM RLS Read Integrity Options..................................................................................... 211
Types of data sets.........................................................................................................................215 EXAMINE users.............................................................................................................................215
Chapter 16. Coding VSAM User-Written Exit Routines...........................................................................221 Guidelines for Coding Exit Routines.................................................................................................. 221 Programming Guidelines................................................................................................................... 222
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Chapter 20. Selecting record formats for Non-VSAM data sets.............................................................265 Format Selection................................................................................................................................ 265 Fixed-length record formats..............................................................................................................266
RELSE—Release an Input Buffer.................................................................................................. 317 TRUNC—Truncate an Output Buffer.............................................................................................317
MB line...........................................................................................................................................328 Planning to use BSAM, BPAM, QSAM and OCE support for XTIOT, uncaptured UCBs, and
UCBs, and DSAB above the line.............................................................................................. 329 Coding the LOC=ANY DCBE option.............................................................................................. 333 Coding the DEVSUPxx option....................................................................................................... 333 Diagnosing problems with BSAM, BPAM, QSAM and OCE support for XTIOT, uncaptured
UCBs, and DSAB above the line.............................................................................................. 334
Setting Up the Enhanced Data Integrity Function....................................................................... 338 Synchronizing the Enhanced Data Integrity Function on Multiple Systems............................... 339 Using the START IFGEDI Command............................................................................................ 339 Bypassing the Enhanced Data Integrity Function for Applications.............................................340 Diagnosing Data Integrity Warnings and Violations.................................................................... 340
PDSEs................................................................................................................................................. 342 Direct Data Sets (BDAM).................................................................................................................... 342 Factors to Consider When Opening and Closing Data Sets...............................................................342 Control of checkpoint data sets on shared DASD volumes.............................................................. 343 System use of search direct for input operations............................................................................. 344
Determining the length of a block when reading with BSAM, BPAM, or BDAM................................361 Writing a Short Format-FB Block with BSAM or BPAM..................................................................... 362 Using Hiperbatch................................................................................................................................363 Processing Extended-Format Sequential Data Sets......................................................................... 363
Processing Large Format Data Sets...................................................................................................369 Characteristics of Large Format Data Sets.................................................................................. 369 Allocating Large Format Data Sets...............................................................................................369 Opening and Closing Large Format Data Sets............................................................................. 370 Migrating to Large Format Data Sets............................................................................................370
Processing a Member of a PDSE........................................................................................................409 Establishing Connections to Members.........................................................................................409 Using the BLDL Macro to Construct a Directory Entry List.......................................................... 410 Using the BSP Macro to Backspace a Physical Record............................................................... 410 Using the Directory Entry Services...............................................................................................410 Using the FIND Macro to Position to the Beginning of a Member...............................................417 Using ISITMGD to Determine Whether the Data Set Is System Managed................................. 417 Using the NOTE Macro to Provide Relative Position....................................................................418 Using the POINT Macro to Position to a Block.............................................................................419 Switching between Members.......................................................................................................419 Using the STOW Macro to Update the Directory..........................................................................420
Retrieving a Member of a PDSE......................................................................................................... 421 Sharing PDSEs.................................................................................................................................... 422
Using HFS Data Sets...........................................................................................................................439 Creating HFS Data Sets................................................................................................................ 439 Creating Additional Directories.................................................................................................... 440
Naming Generation Data Groups for ISO/ANSI Version 3 or Version 4 Labels................................ 461 Creating a New Generation................................................................................................................461
Allocating a Generation Data Set................................................................................................. 461 Passing a Generation Data Set..................................................................................................... 463 Rolling In a Generation Data Set..................................................................................................464 Controlling Expiration of a Rolled-Off Generation Data Set ....................................................... 464
Chapter 31. Using non-VSAM user-written exit routines....................................................................... 473 General Guidance...............................................................................................................................473
Example: Converting a data set......................................................................................................... 559 Example: Issuing a SYNADAF macro.................................................................................................559
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7. Data set with spanned records................................................................................................................... 78
8. Entry-sequenced data set...........................................................................................................................80
10. Record of a key-sequenced data set........................................................................................................83
11. Inserting records into a key-sequenced data set.................................................................................... 83
12. Inserting a logical record into a CI........................................................................................................... 84
13. Fixed-length relative-record data set.......................................................................................................86
16. Control interval in a control area.............................................................................................................. 90
20. VSAM macro relationships......................................................................................................................142
21. Skeleton VSAM program.........................................................................................................................143
23. Determining free space.......................................................................................................................... 150
30. VSAM RLS address and data spaces and requester address spaces....................................................202
31. CICS VSAM non-RLS access................................................................................................................... 204
33. Example of a JRNAD exit Part 1 of 2...................................................................................................... 228
34. Example of a JRNAD exit Part 2 of 2...................................................................................................... 229
35. Example of a SYNAD exit routine........................................................................................................... 238
37. Relation of index entry to data control interval..................................................................................... 254
38. Levels of a prime index........................................................................................................................... 255
41. Format of an index record...................................................................................................................... 259
47. Spanned format-V records for direct data sets..................................................................................... 273
49. Fixed-length records for ISO/ANSI tapes.............................................................................................. 276
50. Nonspanned format-D Records for ISO/ANSI tapes as seen by the program......................................278
51. Spanned variable-length (format-DS) records for ISO/ANSI tapes as seen by the program...............279
52. Reading a sequential data set................................................................................................................ 290
54. Sources and sequence of operations for completing the DCB..............................................................292
55. Record Processed when LEAVE or REREAD is Specified for CLOSE TYPE=T........................................304
56. Constructing a buffer pool from a static storage area........................................................................... 313
57. Constructing a buffer pool using GETPOOL and FREEPOOL..................................................................314
58. Simple buffering with MACRF=GL and MACRF=PM...............................................................................315
59. Simple buffering with MACRF=GM and MACRF=PM..............................................................................316
60. Simple buffering with MACRF=GL and MACRF=PL................................................................................ 316
61. Simple buffering with MACRF=GL and MACRF=PM-UPDAT mode....................................................... 316
62. Parallel processing of three data sets....................................................................................................326
63. JCL, macros, and procedures required to share a data set using multiple DCBs.................................336
64. Macros and procedures required to share a data set using a single DCB.............................................337
65. Creating a Sequential Data Set—Move Mode, Simple Buffering............................................................348
66. Retrieving a Sequential Data Set—Locate Mode, Simple Buffering.......................................................349
67. Like Concatenation Read through BSAM............................................................................................... 353
68. Reissuing a READ or GET for unlike concatenated data sets................................................................ 354
69. One method of determining the length of a record when using BSAM to read undefined-length or blocked records....................................................................................................................................... 362
70. A partitioned data set (PDS)................................................................................................................... 374
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75. Creating Members of a PDS Using STOW...............................................................................................380
76. BLDL list format.......................................................................................................................................381
78. DESERV GET by PDSDE control block structure.................................................................................... 383
79. DESERV GET_ALL control block structure............................................................................................. 384
80. Retrieving several members and subgroups of a PDS without overlapping I/O time and CPU time... 387
81. Reading a member of a PDS or PDSE using asynchronous BPAM.........................................................388
82. Updating a member of a PDS..................................................................................................................390
83. A partitioned data set extended (PDSE).................................................................................................394
84. TTRs for a PDSE member (unblocked records)......................................................................................397
85. TTRs for two PDSE members (LRECL=80, BLKSIZE=800).................................................................... 397
86. Example of how PDSE records are reblocked........................................................................................400
87. Example of reblocking when the block size has been changed............................................................ 400
88. Creating one member of a PDSE............................................................................................................ 406
90. Adding PDSE members serially.............................................................................................................. 408
92. DESERV GET by NAME_LIST control block structure............................................................................412
93. DESERV GET by PDSDE control block structure.................................................................................... 413
97. DESERV UPDATE.....................................................................................................................................417
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99. Using NOTE and FIND to Switch Between Members of a Concatenated PDSE.................................... 420
100. STOW INITIALIZE Example................................................................................................................. 420
103. UNIX directories and files in a file system........................................................................................... 438
104. Edit-Entry panel....................................................................................................................................448
106. ISPF shell panel.................................................................................................................................... 449
107. Using OPUT to copy members of a PDS or PDSE to a UNIX file.......................................................... 450
108. A partitioned concatenation of PDS extents, PDSEs, and UNIX directories.......................................455
109. Status Indicators—BDAM, BPAM, BSAM, and QSAM...........................................................................479
110. Parameter List Passed to DCB Abend Exit Routine............................................................................. 490
111. Recovery Work Area............................................................................................................................. 493
114. IECOENTE Macro Parameter List......................................................................................................... 501
115. IECOEVSE macro parameter list.......................................................................................................... 503
119. Creating a Direct Data Set (Tape-to-Disk)........................................................................................... 518
125. Sequentially updating an indexed sequential data set....................................................................... 536
126. Directly Updating an Indexed Sequential Data Set............................................................................. 539
127. Directly updating an indexed sequential data set with variable-length records................................ 541
128. Adding records to an indexed sequential data set.............................................................................. 543
129. Deleting records from an indexed sequential data set........................................................................544
130. Use of ISAM processing programs....................................................................................................... 550
4. Data set activity for non-system-managed and system-managed data sets............................................28
5. Differences between stripes in sequential and VSAM data sets............................................................... 39
6. CSFSERV resource required for data set encryption..................................................................................60
7. SMS allocation processing based on system levels and allocation request (z/OS V2R2 with OA50569)................................................................................................................................................... 62
10. Entry-sequenced data set processing......................................................................................................81
14. Comparison of ESDS, KSDS, fixed-length RRDS, variable-length RRDS, and linear data sets............... 87
15. Parameters provided by access method services................................................................................. 104
17. Effect of RPL options on data buffers and positioning...........................................................................137
18. Controlling CA reclaim............................................................................................................................ 152
21. RLS open rules, for recoverable or non-recoverable data sets............................................................. 208
22. VSAM user-written exit routines............................................................................................................ 222
24. Contents of registers at entry to EODAD exit routine............................................................................ 225
25. Contents of registers at entry to EXCEPTIONEXIT routine................................................................... 226
26. Contents of registers at entry to JRNAD exit routine.............................................................................227
27. Contents of parameter list built by VSAM for the JRNAD exit...............................................................229
28. Contents of registers at entry to LERAD exit routine............................................................................. 234
29. Contents of registers for RLSWAIT exit routine..................................................................................... 235
31. Conditions when exits to UPAD routines are taken............................................................................... 239
32. Contents of registers at entry to UPAD exit routine...............................................................................239
33. Parameter list passed to UPAD routine..................................................................................................240
34. Communication with user-security-verification routine........................................................................241
35. 31-bit address keyword parameters......................................................................................................244
37. Segment control codes...........................................................................................................................271
39. Optimum and maximum block size supported...................................................................................... 297
40. Rules for setting block sizes for tape data sets or compressed format data sets................................298
41. Buffering technique and GET/PUT processing modes.......................................................................... 317
43. Different conditions for data integrity violations................................................................................... 342
44. Types of sequential data sets on DASD – characteristics and advantages.......................................... 348
45. PDSE and PDS differences......................................................................................................................395
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48. OPEN for UPDAT and Positioning to a Member Decision Table ............................................................424
49. Access methods that UNIX files use...................................................................................................... 439
51. DCB exit routines.................................................................................................................................... 474
57. Exception code bits—QISAM.................................................................................................................. 481
58. Register contents on entry to SYNAD routine—BDAM, BPAM, BSAM, and QSAM................................ 482
59. Register contents on entry to SYNAD routine—BISAM..........................................................................483
60. Register contents on entry to SYNAD routine—QISAM......................................................................... 483
61. DCB exit list format and contents...........................................................................................................486
62. Option mask byte settings......................................................................................................................491
63. Conditions for which recovery can be attempted.................................................................................. 492
65. System response to a user label exit routine return code.....................................................................499
66. Saving and restoring general registers...................................................................................................501
67. Requests for indexed sequential data sets............................................................................................530
68. QISAM error conditions.......................................................................................................................... 551
69. BISAM error conditions.......................................................................................................................... 552
72. ABEND codes issued by the ISAM interface.......................................................................................... 554
75. Output DISP=NEW,OLD.......................................................................................................................... 576
77. Input........................................................................................................................................................578
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About this document
This document is intended for system and application programmers. This document is intended to help you use access methods to process virtual storage access method (VSAM) data sets, sequential data sets, partitioned data sets (PDSs), partitioned data sets extended (PDSEs), z/OS® UNIX files, and generation data sets in the DFSMS environment. This document also explains how to use access method services commands, macro instructions, and JCL to process data sets.
For information about the accessibility features of z/OS, for users who have a physical disability, see Appendix G, “Accessibility,” on page 581.
Major divisions of this document This document is divided into these major parts:
• Part 1 covers general topics for all data sets. • Part 2 covers the processing of VSAM data sets. • Part 3 covers the processing of non-VSAM data sets and UNIX files. • Appendixes cover the following topics:
– Using direct-access labels. – Copying and printing Kanji characters by using the double-byte character set. – Processing direct data sets. – Processing indexed sequential data sets. – Using ISAM programs with VSAM data sets. – Converting character sets.
Required product knowledge To use this document effectively, you should be familiar with the following information:
• IBM support and how it is structured • Assembler language • Job control language (JCL) • Diagnostic techniques
You should also understand how to use access method services commands, catalogs, and storage administration, which the following documents describe.
Topic Document
Access method services commands
z/OS DFSMS Access Method Services Commands describes the access method services commands used to process virtual storage access method (VSAM) data sets.
Catalogs z/OS DFSMS Managing Catalogs describes how to create master and user catalogs.
Storage administration z/OS DFSMSdfp Storage Administration and z/OS DFSMS Implementing System-Managed Storage describe storage administration.
Macros z/OS DFSMS Macro Instructions for Data Sets describes the macros used to process VSAM and non-VSAM data sets.
© Copyright IBM Corp. 1987, 2020 xxix
Topic Document
z/OS UNIX System Services
z/OS UNIX System Services User's Guide describes how to process z/OS UNIX files.
Referenced documents For a complete list of DFSMS documents and related z/OS documents referenced by this document, see the z/OS Information Roadmap. You can obtain a softcopy version of this document and other DFSMS documents from sources listed here.
This document refers to the following additional documents:
Document Title Description
Character Data Representation Architecture Reference and Registry
Document that includes information about coded character set identifiers in the character data representation architecture repository.
z/OS information This information explains how z/OS references information in other documents and on the web.
When possible, this information uses cross document links that go directly to the topic in reference using shortened versions of the document title. For complete titles and order numbers of the documents for all products that are part of z/OS, see z/OS Information Roadmap.
To find the complete z/OS library, go to IBM Knowledge Center (www.ibm.com/support/ knowledgecenter/SSLTBW/welcome).
xxx z/OS: z/OS DFSMS Using Data Sets
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Important: If your comment regards a technical question or problem, see instead “If you have a technical problem” on page xxxi.
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© Copyright IBM Corp. 1987, 2020 xxxi
Summary of changes
This information includes terminology, maintenance, and editorial changes. Technical changes or additions to the text and illustrations for the current edition are indicated by a vertical line to the left of the change.
Summary of changes for z/OS Version 2 Release 4 (V2R4)
New
• Information regarding zHyperLink I/O was added. For more information, see “zHyperLink I/O” on page 164.
• “Advantages of PDSEs” on page 393 was updated with an advantage. • “Virtual storage access method” on page 6 was updated as part of VSAM/zHyperLink functionality
that was added from OA52876.
Changed
• The appendix "Converting data sets" was renamed to "Converting character sets for ISO/ANSI V4 tapes" for clarity.
Summary of changes for z/OS Version 2 Release 3 (V2R3) The following changes are made for z/OS Version 2 Release 3 (V2R3).
New
• Added information for developers of programs that run in supervisor state or system protection key (0 - 7), in “Using access methods in system key programs” on page 306.
• Added information for DADSM partial release for compressed format sequential data sets in “Characteristics of Compressed Format Data Sets” on page 366.
• Added information about new support for accessing read-only data sets, in “Processing data sets on read-only devices” on page 20.
• Added information about new support for z/OS data set encryption, in “Data set encryption” on page 57.
Updated
• “Setting IGDSMSxx PARMLIB values for VSAM RLS data buffering” on page 206 has been updated. • “Using VERIFY to process improperly closed data sets” on page 51 has been updated. • Improved description of SYNAD processing in “Basic Access Methods” on page 485, and “Returning
from the SYNAD routine” on page 485. • Updated information related to 3380 DASD devices, to reflect 3390 DASD information as appropriate.
Removed
• Removed section for 'Building a Generation Data Group' from Chapter 29, “Processing generation data groups,” on page 457.
© Copyright IBM Corp. 1987, 2020 xxxiii
Summary of changes for z/OS Version 2 Release 2 (V2R2) The following changes are made for z/OS Version 2 Release 2 (V2R2).
New
• Added information on using a non-SMS managed VSAM linear data set with extended addressability as a zFS version root, in “Using a non-SMS managed data set for a zFS version root larger than four gigabytes” on page 438.
• Added information on using hiperspace caching for PDSEs, in “Hiperspace caching for PDSE” on page 433.
Changed
• VSAM information was updated in “Acquiring buffers” on page 164, “Using Hiperspace Buffers with LSR” on page 191, and “Deciding the Size of a Virtual Resource Pool” on page 192.
• Space constraint attributes for a data class may now apply to the secondary quantity during allocation, as well as the primary quantity, resulting in more efficient use of space. For more information, refer to “Allocation of data sets with the space constraint relief attributes” on page 41.
Moved
“Using BSAM, BPAM, and QSAM support for XTIOT, uncaptured UCBs, and DSAB above the 16 MB line” on page 328 was moved into this information from a previous edition of DFSMS Using the New Functions.
Deleted
No content was removed from this information.
xxxiv z/OS: z/OS DFSMS Using Data Sets
Part 1. All data sets This topic provides information on general topics for all data sets.
© Copyright IBM Corp. 1987, 2020 1
2 z/OS: z/OS DFSMS Using Data Sets
Chapter 1. Working with data sets
This chapter covers the following topics.
Topic
“Access methods” on page 4
“Direct Access Storage Device (DASD) volumes” on page 8
“Magnetic tape volumes” on page 11
“Data management macros” on page 14
“Data set processing” on page 15
“Distributed Data Management (DDM) attributes” on page 23
“Virtual I/O for temporary data sets” on page 23
“Data set names” on page 24
“Catalogs and volume table of contents” on page 25
A data set is a collection of logically related data and can be a source program, a library of macros, or a file of data records used by a processing program. Data records are the basic unit of information that is used by a processing program. By placing your data into volumes of organized data sets, you can save and process the data. You can also print the contents of a data set or display the contents on a terminal.
Exception: z/OS UNIX files are different from the typical data set because they are byte-oriented rather than record-oriented.
Data storage and management You can store data on secondary storage devices, such as a direct access storage device (DASD) or magnetic tape volume. The term DASD applies to disks or to a mass storage medium on which a computer stores data. A volume is a standard unit of secondary storage. You can store all types of data sets on DASD but only sequential data sets on magnetic tape. Mountable tape volumes can reside in an automated tape library. For information about magnetic tape volumes, see z/OS DFSMS Using Magnetic Tapes. You can also direct a sequential data set to or from spool, a UNIX file, a TSO/E terminal, a unit record device, virtual I/O (VIO), or a dummy data set.
Each block of data on a DASD volume has a distinct location and a unique address, making it possible to find any record without extensive searching. You can store and retrieve records either directly or sequentially. Use DASD volumes for storing data and executable programs, including the operating system itself, and for temporary working storage. You can use one DASD volume for many different data sets, and reallocate or reuse space on the volume.
Data management is the part of the operating system that organizes, identifies, stores, catalogs, and retrieves all the information (including programs) that your installation uses. Data management does these main tasks:
• Sets aside (allocates) space on DASD volumes. • Automatically retrieves cataloged data sets by name. • Mounts magnetic tape volumes in the drive. • Establishes a logical connection between the application program and the medium. • Controls access to data.
Working with Data Sets
• Transfers data between the application program and the medium.
System-managed data sets The Storage Management Subsystem (SMS) is an operating environment that automates the management of storage. Storage management uses the values that are provided at allocation time to determine, for example, on which volume to place your data set, and how many tracks to allocate for it. Storage management also manages tape data sets on mountable volumes that reside in an automated tape library. With SMS, users can allocate data sets more easily.
The data sets allocated through SMS are called system-managed data sets or SMS-managed data sets. For information about allocating system-managed data sets, see Chapter 2, “Using the Storage Management Subsystem,” on page 27. If you are a storage administrator, also see z/OS DFSMSdfp Storage Administration for information about using SMS.
Distributed FileManager With Distributed FileManager (DFM) target server, applications running on a processor with the DFM source server can create or access certain types of SMS-managed data sets. They can also access certain types of non-SMS-managed data sets on an System/390® processor running DFSMS, with the DFM target server. See z/OS DFSMS DFM Guide and Reference for details about the supported data set types and a discussion of considerations in making them available for remote access. Also, see “Distributed Data Management (DDM) attributes” on page 23.
Access methods An access method defines the technique that is used to store and retrieve data. Access methods have their own data set structures to organize data, macros to define and process data sets, and utility programs to process data sets.
Access methods are identified primarily by the data set organization. For example, use the basic sequential access method (BSAM) or queued sequential access method (QSAM) with sequential data sets. However, there are times when an access method identified with one organization can be used to process a data set organized in a different manner. For example, a sequential data set (not extended- format data set) created using BSAM can be processed by the basic direct access method (BDAM), and vice versa. Another example is UNIX files, which you can process that uses BSAM, QSAM, basic partitioned access method (BPAM), or Virtual Storage Access Method (VSAM).
Basic Direct Access Method BDAM arranges records in any sequence your program indicates, and retrieves records by actual or relative address. If you do not know the exact location of a record, you can specify a point in the data set where a search for the record is to begin. Data sets organized this way are called direct data sets.
Optionally, BDAM uses hardware keys. Hardware keys are less efficient than the optional software keys in virtual sequential access method (VSAM).
Related reading: See the following material:
• “Track format” on page 8 • Appendix C, “Processing direct data sets,” on page 515
Basic Partitioned Access Method Basic partitioned access method (BPAM) arranges records as members of a partitioned data set (PDS) or a partitioned data set extended (PDSE) on DASD. You can use BPAM to view a UNIX directory and its files as if it were a PDS. You can view each PDS, PDSE, or UNIX member sequentially with BSAM or QSAM. A PDS or PDSE includes a directory that relates member names to locations within the data set. Use the PDS, PDSE, or UNIX directory to retrieve individual members. For program libraries (load modules and program objects), the directory contains program attributes that are required to load and rebind the
member. Although UNIX files can contain program objects, program management does not access UNIX files through BPAM.
The following describes some of the characteristics of PDSs, PDSEs, and UNIX files: Partitioned data set
PDSs can have any type of sequential records. Partitioned data set extended
A PDSE has a different internal storage format than a PDS, which gives PDSEs improved usability characteristics. You can use a PDSE in place of most PDSs, but you cannot use a PDSE for certain system data sets.
z/OS UNIX files UNIX files are byte streams and do not contain records. BPAM converts the bytes in UNIX files to records. You can use BPAM to read but not write to UNIX files. BPAM access is like BSAM access.
Basic Sequential Access Method BSAM arranges records sequentially in the order in which they are entered. A data set that has this organization is a sequential data set. The user organizes records with other records into blocks. This is basic access. You can use BSAM with the following data types:
• basic format sequential data sets (before z/OS 1.7 these were known as sequential data sets or more accurately as non-extended-format sequential data sets)
• large format sequential data sets • extended-format data sets • z/OS UNIX files
Extended-format data sets have an internal storage format that is different from data sets that are not extended format. The internal storage format for extended-format data sets provides more usability characteristics, and can have better performance if the data set is striped. You can choose for an extended-format data set to be any combination of:
• striped • encrypted • compressed format • or none of those.
Extended-format data sets must be SMS-managed.
Data-in-Virtual (DIV) The data-in-virtual (DIV) macro provides access to VSAM linear data sets. For more information, see z/OS MVS Programming: Assembler Services Guide. You can also use window services to access linear data sets, as described in that information.
Indexed Sequential Access Method ISAM refers to two access methods: basic indexed sequential access method (BISAM) and queued indexed sequential access method (QISAM). Data sets processed by ISAM are called indexed sequential data sets. Starting in z/OS V1R7, you cannot create, open, copy, convert, or dump indexed sequential (ISAM) data sets. You can delete or rename them. You can use an earlier release of z/OS to convert them to VSAM data sets.
Important: Do not use ISAM. You should convert all indexed sequential data sets to VSAM data sets. See Appendix D, “Using the Indexed Sequential Access Method,” on page 523.
Object Access Method Object access method (OAM) processes very large, named byte streams (objects) that have no record boundary or other internal orientation. These objects can be recorded in a Db2 database, file system,
Chapter 1. Working with data sets 5
optical storage volume, or tape storage volume. OAM uses SMS policies to provide information lifecycle management for these objects. For information about OAM, see z/OS DFSMS OAM Application Programmer's Reference and z/OS DFSMS OAM Planning, Installation, and Storage Administration Guide for Object Support.
Queued Sequential Access Method QSAM arranges records sequentially in the order that they are entered to form sequential data sets, which are the same as those data sets that BSAM creates. The system organizes records with other records. QSAM anticipates the need for records based on their order. To improve performance, QSAM reads these records into storage before they are requested. This is called queued access. You can use QSAM with the following data types:
• sequential data sets • basic format sequential data sets (before z/OS 1.7 these were known as sequential data sets or more
accurately as non-extended-format sequential data sets) • large format sequential data sets • extended-format data sets • z/OS UNIX files
Extended-format data sets have an internal storage format that is different from data sets that are not extended format. The internal storage format for extended-format data sets provides more usability characteristics, and can have better performance if the data set is striped. You can choose for an extended-format data set to be any combination of:
• striped • encrypted • compressed format • or none of those.
Extended-format data sets must be SMS-managed.
Virtual storage access method VSAM arranges records by an index key, relative record number, or relative byte addressing. VSAM is used for direct or sequential processing of fixed-length and variable-length records on DASD. Data that is organized by VSAM is cataloged for easy retrieval and is stored in one of five types of data sets.
• Entry-sequenced data set (ESDS). Contains records in the order in which they were entered. Records are added to the end of the data set and can be accessed.
• Key-sequenced data set (KSDS). Contains records in ascending collating sequence. Records can be accessed by a field, called a key, or by a relative byte address.
• Linear data set (LDS). Contains data that has no record boundaries. Linear data sets contain none of the control information that other VSAM data sets do. Linear data sets must be cataloged in a catalog.
• Relative record data set (RRDS). Contains records in relative record number order, and the records can be accessed only by this number. There are two types of relative record data sets.
Fixed-length RRDS: The records must be of fixed length. Variable-length RRDS: The records can vary in length.
Throughout this document, the term RRDS refers to both types of relative record data sets, unless they need to be differentiated.
• z/OS UNIX files. A UNIX file can be accessed as if it were a VSAM entry-sequenced data set (ESDS). Although UNIX files are not stored as entry-sequenced data sets, the system attempts to simulate the characteristics of such a data set. To identify or access a UNIX file, specify the path that leads to it.
Any type of VSAM data set can be in extended format. Extended-format data sets have a different internal storage format than data sets that are not extended. This storage format gives extended-format data sets
additional usability characteristics and possibly better performance due to striping. You can choose for an extended-format key-sequenced data set to be in the compressed format or encrypted format or both. Extended-format data sets must be SMS managed. You cannot use an extended-format data set for certain system data sets.
Requirement: Do not use BISAM or QISAM. Use VSAM instead.
VSAM data set performance can benefit from using the IBM DS888x zHyperlink technology, also known as synchronous I/O. zHyperLink can achieve significant I/O latency improvements for read requests when using non-linear VSAM data sets. When zHyperLink is enabled on the system and a control unit (CI) of data is in the control unit cache, a VSAM read request stays synchronous while the CI is retrieved with a latency time of 20 to 30 microseconds, significantly better than the more than 100-microsecond latency of traditional DASD I/O. While zHyperLink improves latency time, it also incurs small additional CPU utilization. VSAM and VSAM RLS users should monitor the tradeoff, as well as the SMF42 subtypes 5 and 6 counts that are related to zHyperLink ('syncIO')
zHyperLink I/O is disabled system-wide by default. To do zHyperLink I/O for a read request, all of the following conditions must be met and checked by VSAM and VSAM RLS before they issue a zHyperLink I/O request:
• The user has issued the SETIOS ZHYPERLINK OPER=[ALL|READ] command, or SYS1.PARMLIB(IECIOSxx) specifies ZHYPERLINK,OPER=[ALL|READ]. NONE is the default in z/OS 2.1 through z/OS 2.3. ALL is the default.
• SYS1.PARMLIB(IGDSMSxx) or the SETSMS command specifies VSAM_ZHYPERLINK(YES), where NO is the default.
• The data sets must be set to be zHyperLink eligible. This is done by specifying zHyperLink Eligible for Read: YES in the storage class for the data sets.
• V SMS,DSNAME(datasetname) ZHLREAD=YES is issued to make read I/O for the specified data set synchronous, overriding the specification in the storage class for that data set. Default is not to override the storage class specification.
• The RLS or VSAM-built buffer, or the VSAM user-provided buffer (such as VSAM user buffering) that receives the CI must on a quadword boundary.
• zHyperLink I/O needs to have the internal Bypass Extent Serialization set ON. RLS and VSAM set it.
When all of those conditions are met and VSAM or VSAM RLS initiates a zHyperLink I/O request, the I/O driver can still do asynchronous I/O because the CI is larger than 4 KB, or the CI is not found in control unit cache. In that situation, VSAM RLS accumulates the suspend elapsed time for the asynchronous DASD I/O for the data set. The counts are recorded in SMF42 subtype 6 fields S42SNAvgARDelay S42SNARDelayCount to help the users understand the potential performance benefits of enabling zHyperLink reads for VSAM RLS data sets. Non-RLS VSAM does not do such count.
Access to z/OS UNIX files Programs can access the information in UNIX files through z/OS UNIX System Services (z/OS UNIX) calls, such as open(pathname), read(file descriptor), and write(file descriptor). Programs can also access the information in UNIX files through the BSAM, BPAM, QSAM, and VSAM access methods. When you use BSAM or QSAM, a UNIX file is simulated as a single-volume sequential data set. When you use VSAM, a UNIX file is simulated as an ESDS. When you use BPAM, a UNIX directory and its files are simulated as a partitioned data set directory and its members.
You can use the following types of UNIX files with the access methods:
• Regular files, including files accessed through Network File System (NFS), temporary file system (TFS), HFS, or z/OS File System (zFS)
• Character special files • First-in-first-out (FIFO) special files • Symbolic links
You cannot use the following types of UNIX files with the access methods:
• UNIX directories, except indirectly through BPAM • External links
Files can reside on other systems. The access method user can use NFS to access them.
Selection of an access method In selecting an access method for a data set, consider the organization of the data set, what you need to specify through macros, and the device type:
• VSAM data sets, PDSEs, PDSs, extended-format data sets, direct data sets, and UNIX files must be stored on DASD volumes.
• Sequential data sets can be on DASD or tape volumes, or these data sets can be read from or written to a unit record device or TSO/E terminal. They can be spooled data sets. Spooled data sets named SYSOUT can be directed over a network. Sequential data sets also can be dummy data sets.
In addition, you should select a data organization according to the type of processing you want to do: sequential or direct. For example, RRDSs or key-sequenced data sets are best for applications that use only direct access, or both direct and sequential access. Sequential or VSAM entry-sequenced data sets are best for batch processing applications and for sequential access.
Restriction: You cannot process VSAM data sets with non-VSAM access methods, although you can use DIV macros to access linear data sets. You cannot process non-VSAM data sets except for UNIX files with VSAM.
See z/OS TSO/E Command Reference for information about using BSAM and QSAM to read from and write to a TSO/E terminal in line mode.
Direct Access Storage Device (DASD) volumes Although DASD volumes differ in physical appearance, capacity, and speed, they are similar in data recording, data checking, data format, and programming. The recording surface of each volume is divided into many concentric tracks. The number of tracks and their capacity vary with the device.
DASD labels The operating system uses groups of labels to identify DASD volumes and the data sets they contain. Application programs generally do not use these labels directly. DASD volumes must use standard labels. Standard labels include a volume label, a data set label for each data set, and optional user labels. A volume label, stored at track 0 of cylinder 0, identifies each DASD volume.
A utility program initializes each DASD volume before it is used on the system. The initialization program generates the volume label and builds the volume table of contents (VTOC). The VTOC is a structure that contains the data set labels.
See Appendix A, “Using direct access labels,” on page 507 for information about direct access labels.
Track format Information is recorded on all DASD volumes in a standard format. This format is called count-key data (CKD) or extended count-key data (ECKD).
Each track contains a record 0 (also called track descriptor record or capacity record) and data records. Historically, S/390® hardware manuals and software manuals have used inconsistent terminology to refer to units of data written on DASD volumes. Hardware manuals call them records. Software manuals call them blocks and use “record” for something else. The DASD sections of this document use both terms as appropriate. Software records are described in Chapter 6, “Organizing VSAM data sets,” on page 75 and Chapter 20, “Selecting record formats for Non-VSAM data sets,” on page 265.
For these data formats, one or more of the following is true:
• Each VSAM control interval consists of one or more contiguous blocks. Control intervals are grouped into control areas.
• Each non-VSAM block contains part of a record or one or more records. Examples of these programming interfaces are BSAM, BDAM, and EXCP.
• Each VSAM record occupies multiple control intervals or all or part of a control interval. Each non-VSAM record occupies multiple blocks or all or part of a block. An example is QSAM.
• The application program might regard byte streams as being grouped in records. The program does not see blocks. Examples of such programs include UNIX files and OAM objects.
The process of grouping records into blocks is called blocking. The extraction of records from blocks is called unblocking. Blocking or unblocking might be done by the application program or the operating system. In z/OS UNIX, blocking means suspension of program execution.
Under certain conditions, BDAM uses the data area of record zero to contain information about the number of empty bytes following the last user record on the track. This is called the track descriptor record.
The following figure shows the two different data formats, count-data and count-key-data, only one of which can be used for a particular data set. An exception is PDSs that are not PDSEs. The directory blocks are in count-key-data format, and the member blocks normally are in count-data format.
Count Data Count Data Count Data
Count Data Count DataKey Count DataKey. . .
. . .
Figure 1. DASD volume track formats
In Count-Data Format, records are formatted without keys. The key length is 0. The count area contains 8 bytes that identify the location of the block by cylinder, head, and record numbers, and its data length.
In Count-Key-Data Format, the blocks are written with hardware keys. The key area (1 - 255 bytes) contains a record key that specifies the data record, such as the part number, account number, sequence number, or some other identifier.
In data sets, only BDAM, BSAM, EXCP, and PDS directories use blocks with hardware keys. Outside data sets, the VTOC and the volume label contain hardware keys.
Tip: The use of hardware keys is less efficient than the use of software keys (which VSAM uses).
Track overflow The operating system no longer supports the track overflow feature. The system ignores any request for it.
VSAM record addressing You identify VSAM records by their key, record number, or relative byte address in the data set. See “Selection of VSAM data set types” on page 79.
Actual and relative addressing with non-VSAM access methods With certain access methods, you can access data non-sequentially. You can use addresses to identify block locations. Use two types of addresses to store and retrieve data on DASD volumes: actual addresses and relative addresses. When sequentially processing a multiple volume data set with a BSAM DCB, except for extended-format data sets, you can refer to only records of the current volume.
Actual addresses
When the system returns the actual address of a block on a direct access volume to your program, it is in the form MBBCCHHR, in which the characters represent the following values: M
1-byte binary number that specifies the relative extent number. Each extent is a set of consecutive tracks that are allocated for the data set.
BBCCHH Three 2-byte binary numbers that specify the cell (bin), cylinder, and head number for the block (its track address). The cylinder and head numbers are recorded in the count area for each block. All DASDs require that the bin number (BB) be zero.
R 1-byte binary number that specifies the relative block number on the track. The block number is also recorded in the count area.
If your program stores actual addresses in your data set, and you refer to those addresses, the data set must be treated as unmovable. Data sets that are unmovable cannot reside on system-managed volumes.
If you store actual addresses in another data set, those addresses become nonvalid if the first data set is moved or migrated. Although you can mark the data set with the unmovable attribute in DSORG that prevents the data set from being SMS-managed.
Relative addresses
BDAM, BSAM, and BPAM optionally use relative addresses to identify blocks in the data set.
BSAM and BPAM relative addresses are relative to the data set on the current volume. BDAM relative addresses are relative to the data set and go across all volumes.
BDAM relative block addresses. The relative block address is a 3-byte binary number that shows the position of the block, starting from the first block of the data set. Allocation of noncontiguous sets of blocks does not affect the number. The first block of a data set always has a relative block address of 0.
BDAM, BSAM, and BPAM Relative Track Addresses. With BSAM, you can use relative track addresses in basic or large format data sets. With BPAM, you can use relative track addresses in PDSs. The relative track address has the form TTR or TTTR: TT or TTT
An unsigned two-byte or three-byte binary number specifying the position of the track starting from the first track that is allocated for the data set. It always is two bytes with BDAM and it is two bytes with BSAM and BPAM when you do not specify the BLOCKTOKENSIZE=LARGE parameter on the DCBE macro. It is three bytes with BSAM and BPAM when you specify the BLOCKTOKENSIZE=LARGE parameter on the DCBE macro. The value for the first track is 0. Allocation of noncontiguous sets of tracks does not affect the relative track number.
R 1-byte binary number specifying the number of the block starting from the first block on the track TT or TTT. The R value for the first block of data on a track is 1.
With most DASD devices, a data set can contain more than 32 767 tracks. That is X'7FFF'. Therefore, assembler halfword instructions operating on two-byte numbers could result in non-valid data being processed.
Relative Block Addresses for Extended-Format Data Sets. For extended-format data sets, block locator tokens (BLTs) provide addressing capability. You can use a BLT transparently, as if it were a relative track record (TTR). The NOTE macro returns a 4-byte value. If you do not code BLOCKTOKENSIZE=LARGE on
the DCBE macro, then the three high-order bytes are the BLT value and the fourth byte is a zero. If you code BLOCKTOKENSIZE=LARGE on the DCBE macro, then the four bytes are the BLT value. Your program uses the value from the NOTE macro as input to the POINT macro, which provides positioning within a sequential data set through BSAM. The BLT is essentially the relative block number (RBN) within each logical volume of the data set (where the first block has an RBN of 1). For compressed format data sets, the relative block numbers represent uncompressed simulated blocks, not the real compressed blocks.
A multistriped data appears to the user as a single logical volume. Therefore, for a multistriped data set, the RBN is relative to the beginning of the data set and incorporates all stripes.
Relative Track Addresses for PDSEs. For PDSEs, the relative track addresses (TTRs) do not represent the actual track and record location. Instead, the TTRs are tokens that define the record's position within the data set. See “Relative track addresses (TTR)” on page 397 for a description of TTRs for PDSE members and blocks. Whether the value is three bytes or four bytes depends on whether you specify BLOCKTOKENSIZE=LARGE on the DCBE macro.
Relative Track Addresses for UNIX files. For UNIX files, the relative track addresses (TTRs) do not represent the actual track and record location. Instead, the TTRs are tokens that define a BPAM logical connection to a UNIX member or the record's position within the file. Whether the value is three bytes or four bytes depends on whether you specify BLOCKTOKENSIZE=LARGE on the DCBE macro.
Magnetic tape volumes This topic discusses using tape labels and specifying the file sequence number for data sets that are stored on magnetic tape volumes.
Because data sets on magnetic tape devices must be organized sequentially, the procedure for allocating space is different from allocating space on DASD. All data sets that are stored on a given magnetic tape volume must be recorded in the same density. See z/OS DFSMS Using Magnetic Tapes for information about magnetic tape volume labels and tape processing.
For information about nonstandard label processing routines, see z/OS DFSMS Installation Exits.
Using magnetic tape labels The operating system uses groups of labels to identify magnetic tape volumes and the data sets that they contain. Application programs generally do not use these labels directly. Magnetic tape volumes can have standard or nonstandard labels, or they can be unlabeled. DASD volumes must use standard labels. Standard labels include a volume label, a data set label for each data set, and optional user labels. A volume label, which is stored at track 0 of cylinder 0, identifies each DASD volume.
International Organization for Standardization (ISO) and the American National Standards Institute (ANSI) tape labels are similar to IBM standard labels. ASCII permits data on magnetic tape to be transferred from one computer to another, even though the two computers can be products of different manufacturers. IBM standard labels are coded in the extended binary-coded-decimal interchange code (EBCDIC). ISO/ANSI labels are coded in the American National Standard Code for Information Interchange (ASCII).
Specifying the file sequence number When a new data set is to be placed on a magnetic tape volume, you must specify the file sequence number if the data set is not the first one on the reel or cartridge. The maximum value of the file sequence number of a data set on a tape volume is 65535 for the following tapes:
• Standard label (SL) tapes • Standard user label (SUL) tapes • Leading tape mark (LTM) tapes • Unlabeled (NL) tapes • Bypass label processing (BLP) tapes
Restriction: The ISO/ANSI (AL) labeled tapes do not allow a file sequence number greater than 9999.
For additional information about using file sequence numbers, see z/OS DFSMS Using Magnetic Tapes.
You can specify the file sequence number in one of the following ways:
• Code the file sequence number as the first value of the LABEL keyword on the DD statement or using the DYNALLOC, macro for dynamic allocation.
• Catalog each data set using the appropriate file sequence number and volume serial number. Issue the OPEN macro because the catalog provides the file sequence number.
OPEN uses the file sequence number from the catalog if you do not specify it on the DD statement or dynamic allocation.
• You can use the RDJFCB macro to read the job file control block (JFCB), set the file sequence number in the JFCB, and issue the OPEN, TYPE=J macro for a new or uncataloged data set. The maximum file sequence number is 65535. This method overrides other sources of the file sequence number.
For more information on the OPEN macro, see z/OS DFSMS Macro Instructions for Data Sets. For more information on the RDJFCB and OPEN, TYPE=J macros, see z/OS DFSMSdfp Advanced Services. For more information on IEHPROGM, see z/OS DFSMSdfp Utilities.
Example of creating a tape data set with a file sequence number greater than 9999
The following example shows how to use the OPEN,TYPE=J and RDJFCB macros to create a cataloged tape data set with a file sequence number of 10011. The file sequence number is stored in the JFCB. In the JCL statement, specify the LABEL=(1,labeltype) parameter, where labeltype is the type of tape label such as SL or NL. This example works with any file sequence number from 1 to 65535 if the previous file exists on the specified tape or on a volume that is named in the JFCB or JFCB extension. When the system unallocates the data set, it creates an entry for the data set in the catalog.
Example:
//* STEP05 //* Create a tape data set with a file sequence number of 10011. //* Update the file sequence number (FSN) in JFCB using OPEN TYPE=J macro. //*-------------------------------------------------------------------- //STEP05 EXEC ASMHCLG //C.SYSIN DD * . . . L 6,=F'10011' CREATE FSN 10011 RDJFCB (DCBAD) READ JFCB STCM 6,B'0011',JFCBFLSQ STORE NEW FSN IN JFCB OPEN (DCBAD,(OUTPUT)),TYPE=J CREATE FILE PUT DCBAD,RECORD WRITE RECORD DCBAD CLOSE CLOSE FILE . . . DCBDCB DDNAME=DD1,DSORG=PS,EXLST=LSTA,MACRF=PM,LRECL=80,RECFM=FB LSTA DS 0F RJFCB EXIT LIST DC AL1(EXLLASTE+EXLRJFCB) CODE FOR JFCB (X'87') DC AL3(JFCBAREA) POINTER TO JFCB AREA JFCBAREA EQU * 176 bytes for copy of JFCB * The IEFJFCBN does not define a DSECT. This continues the CSECT. IEFJFCBN DEFINE THE JFCB FIELDS RECORD DC CL80'RECORD10011' RECORD AREA IHAEXLST , Define symbols for DCB exit list END //* JCL FOR ALLOCATING TAPE DATA SET //DD1 DD DSN=DATASET1,UNIT=TAPE,VOL=SER=TAPE01,DISP=(NEW,CATLG), // LABEL=(1,SL)
The output displays information about the new tape data set with a file sequence number of 10011:
IEC205I DD1,OCEFS005,G.STEP05,FILESEQ=10011, COMPLETE VOLUME LIST, DSN=DS10011,VOLS=TAPE01,TOTALBLOCKS=1
Example of creating a tape data set using any file Sequence number
The following example shows how to use the OPEN macro to create several tape data sets with file sequence numbers ranging from 1 to 10010. In the JCL statement, specify the LABEL=(fsn,labeltype) parameter, where fsn is the file sequence number and labeltype is the type of tape label such as SL or NL.
Example:
//* STEP06 //* Create files 1 through 10010 on a single volume. //*-------------------------------------------------------------- //STEP06 EXEC ASMHCLG //C.SYSIN DD * . . . L 6,=F'10010' CREATE 10010 FILES LA 5,1 START AT FILE 1 AND DS1 RDJFCB (DCBAD) READ JFCB MVC JFCBAREA(44),=CL44'DS' DSNAME IS 'DSfsn' WHERE * fsn IS FSN 1 TO 10010 * ------------------------------------------------------------- * This loop creates file sequence numbers from 1 to 10010. * ------------------------------------------------------------- LOOP EQU * STCM 5,B'0011',JFCBAREA+68 STORE NEW FSN IN JFCB CVD 5,WORKAREA UPDATE DSNAME UNPK JFCBAREA+2(5),WORKAREA(8) LOAD JFCB OI JFCBAREA+6,X'F0' SET DSfsn MVC RECORD+6(5),JFCBAREA+2 MOVE FSN INTO RECORD * RECORD FORMAT IS 'RECORDfsn' OPEN (DCBAD, (OUTPUT)),TYPE=J CREATE FILE NUMBER PUT DCBAD,RECORD WRITE RECORD CLOSE (DCBAD,LEAVE) CLOSE FILE NUMBER CONTIN EQU * RDJFCB (DCBAD) READ JFCB SR 5,5 ICM 5,B'0011',JFCBAREA+68 GET CURRENT FSN LA 5,1(5) INCREMENT FSN BCT 6,LOOP CONTINUE PROCESSING UNTIL DONE . . . * DEFINITIONS DS 0D SAVE DC 18F'0' DCBAD DCB DDNAME=DD1,DSORG=PS,EXLST=LSTA,MACRF=PM,BLKSIZE=80,RECFM=F LSTA DS 0F RJFCB EXIT LIST DC X'87' DC AL3(JFCBAREA) JFCBAREA DC 50F'0' JFCB AREA RECORD DC CL80'RECORD' RECORD AREA DS 0D WORKAREA DC 2F'0' WORK AREA END /* * JCL FOR ALLOCATING TAPE DATA SET
This excerpt from the output shows information about the tape data set with a file sequence number of 9999:
IEC205I DD1,OCEFS001,G.STEP06,FILESEQ=09999, COMPLETE VOLUME LIST, DSN=DS09999,VOLS=TAPE01,TOTALBLOCKS=1
Identifying unlabeled tapes When you want to store a data set on unlabeled tape volumes, the system needs a volume serial number to identify each volume. If the data set is in an automatic tape library, the system uses the volume serial number that is encoded in the bar code on the outside of each cartridge. If the data set is not in an automatic tape library, it is advisable to specify enough volume serial numbers to contain the data set. If you do not specify any volume serial numbers or do not specify enough of them, the system or a tape management system assigns a serial number to each unidentified volume. If the system assigns a serial number, the serial number is in the form Lxxxyy, in which xxx is the data set sequence number and yy is the volume sequence number for the data set.
If you want to catalog or pass data sets that reside on unlabeled volumes, specify the volume serial numbers for the required volumes. Specifying the volume serial numbers ensures that data sets residing
on multiple volumes are not cataloged or passed with duplicate volume serial numbers. Retrieving such data sets can give unpredictable errors.
Using tape marks A tape mark must follow each data set and data set label group. Tape marks cannot exist within a data set. When a program writes data on a standard labeled or unlabeled tape, the system automatically reads and writes labels and tape marks. Two tape marks follow the last trailer label group on a standard-label volume. On an unlabeled volume, the two tape marks appear after the last data set.
When a program writes data on a nonstandard labeled tape, the installation must supply routines to process labels and tape marks and to position the tape. If you want the system to retrieve a data set, the installation routine that creates nonstandard labels must write tape marks. Otherwise, tape marks are not required after nonstandard labels because installation routines manage positioning of the tape volumes.
Data management macros You can use macros to process all the data set types supported by the access methods just described. Macros control data set allocation, input and output, the buffering techniques used, and data security. See z/OS DFSMS Macro Instructions for Data Sets for information about data management macros. See z/OS DFSMSdfp Advanced Services for information about system programming macros.
Table 1 on page 14 contains a summary of data management access methods:
Table 1. Data management access methods
Data Set Organization Basic Queued VSAM
Direct BDAM
ESDS VSAM
KSDS VSAM
Partitioned (see Note 2) BPAM, BSAM (see Note 3)
QSAM
Sequential (see Note 5) BSAM QSAM
z/OS UNIX file (see Note 6) BSAM (see Note 7) QSAM (see Note 7) VSAM (see Note 8)
Note:
1. The data-in-virtual (DIV) macro, which is used to access a linear data set, is described in z/OS MVS Programming: Assembler Services Guide.
2. PDSs and PDSEs are both partitioned organization data sets. 3. BSAM and QSAM cannot be used to create or modify user data in directory entries. 4. Refers to fixed-length and variable-length RRDSs. 5. Sequential data sets and extended-format data sets are both sequential organization data sets. 6. A UNIX file can be in any type of z/OS UNIX file system such as HFS, NFS, TFS, or zFS. 7. When you access a UNIX file with BSAM or QSAM, the file is simulated as a single-volume sequential
data set. 8. When you access a UNIX file with VSAM, the file is simulated as an ESDS.
Data sets can also be organized as PDSE program libraries. PDSE program libraries can be accessed with BSAM, QSAM, or the program management binder. The first member written in a PDSE library determines the library type, either program or data.
Data set processing To process a data set, first allocate it (establish a link to it), then access the data using macros for the access method that you have chosen. For information about accessing UNIX files, see “Processing UNIX files with an access method” on page 19.
Allocating data sets Allocate means either or both of two things:
• To set aside (create) space for a new data set on a disk. • To establish a logical link between a job step and any data set.
You can use any of the following methods to allocate a data set.
For information about these methods, see Chapter 2, “Using the Storage Management Subsystem,” on page 27.
Access method services
You can define data sets and establish catalogs by using a multifunction services program called access method services. Use the following commands with all data sets.
Table 2. Access method services commands
Command Description
ALTER Change the attributes of a data set
DEFINE NONVSAM Catalog a data set
DELETE Delete a data set
LISTCAT List catalog entries
PRINT Print a data set
For information about access method services commands see z/OS DFSMS Access Method Services Commands.
ALLOCATE command
You can issue the ALLOCATE command either through access method services or TSO/E to define VSAM and non-VSAM data sets.
For information about TSO commands, see z/OS TSO/E Command Reference.
Dynamic allocation
You can allocate VSAM and non-VSAM data sets using the DYNALLOC macro with the SVC 99 parameter list.
For information about dynamic allocation, see z/OS MVS Programming: Authorized Assembler Services Guide.
JCL
All data sets can be defined directly through JCL.
Related reading: For information about using JCL, see z/OS MVS JCL Reference and z/OS MVS JCL User's Guide.
Processing data sets through programs Programs process data sets in the following sequence:
1. Allocate the data set to establish the logical link between a program and a data set. You can do this either outside the program with JCL or the TSO ALLOCATE command or inside the program with dynamic allocation.
2. Open the data set, identifying it with a DDNAME. 3. Do reads and writes using an access method. 4. Close the data set. 5. Deallocate the data set. There are three ways to do this:
• For non-VSAM data sets only, specifying FREE=CLOSE when closing the data set. (The FREE=CLOSE parameter is ignored for VSAM data sets.)
• Your program can call dynamic deallocation. • During the step termination process, the operating system automatically deallocates any remaining
allocated data sets.
Using access methods All the access methods described in this document allow you to do the following:
• Share a data set among different systems, different jobs in a single system, multiple access method control blocks (ACBs) or data control blocks (DCBs) in a task, or different subtasks in an address space. See Chapter 12, “Sharing VSAM data sets,” on page 177 for information about sharing a VSAM data set. See Chapter 23, “Sharing non-VSAM data sets,” on page 335 for information about sharing a non-VSAM data set.
• Share buffers and control blocks among VSAM data sets. See Chapter 13, “Sharing resources among VSAM data sets,” on page 191.
• Provide user exit routines to analyze logical and physical errors, and to perform end-of-data processing. See Chapter 31, “Using non-VSAM user-written exit routines,” on page 473 and Chapter 16, “Coding VSAM User-Written Exit Routines,” on page 221.
• Back up and recover data sets. See Chapter 4, “Backing up and recovering data sets,” on page 47. • Maintain data security and integrity. See Chapter 5, “Prot

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