disk and tape fundamentals

8/7/2019 Disk and Tape Fundamentals

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Instruction, Research & Infrastructure Support, Arizona State University

IBM Mainframe July 2002

Disk and Tape Fundamentals

Table of Contents

MVS -i- Disk and Tape

1. INTRODUCTION .............................................................................................................. 1

1.1 Abstract ......................................................................................................................... 1

1.2 Update Information ..................................................................................................... 1

2. DATA SET BASICS............................................................................................................ 1

2.1 ASCII and EBCDIC Character Sets ............................................................................. 1

2.2 Blocking......................................................................................................................... 2

2.3 Record Format .............................................................................................................. 2

2.4 Data Sets........................................................................................................................ 3

2.4.1 Sequential Data Sets .............................................................................................. 32.4.2 Partitioned Data Sets............................................................................................. 4

3. MECHANICS OF DISK AND TAPE................................................................................ 5

3.1 External Storage Devices ............................................................................................. 5

3.2 Disk Volumes................................................................................................................ 5

3.2.1 Tracks, Cylinders, and Extents ............................................................................. 5

3.2.2 Volume Table of Contents .................................................................................... 6

3.3 Tape Volumes ............................................................................................................... 6

4. USING DISK....................................................................................................................... 8

4.1 MVS Accounts .............................................................................................................. 8

4.1.1 Account Types ....................................................................................................... 8

4.1.2 Disk Space Accounting.......................................................................................... 8

4.2 Estimating the Size of a Data Set ................................................................................ 9

4.2.1Est imating Space for Card-Image Data ............................................................... 9

4.2.2 Estimating Space for Variable-Format Data...................................................... 10

4.2.3 Estimating Space for SAS and SPSS Data Sets.................................................. 10

4.3 Choosing an Efficient Blocksize ................................................................................ 10

4.4 JCL for Disk Data Sets................................................................................................ 11

4.4.1 SPACE Parameter for Sequential Data Sets....................................................... 12

4.4.2 SPACE Parameter for Partitioned Data Sets ..................................................... 134.5 Creating a Data Set ..................................................................................................... 14

4.6 Condensing a Partitioned Data Set ........................................................................... 14

4.7 Making a Data Set Larger .......................................................................................... 15

4.8 Making A Data Set Smaller ....................................................................................... 15

5. USING TAPE.................................................................................................................... 15

5.1 Obtaining a New Tape ............................................................................................... 15

5.2 Tapes from Another Institution ................................................................................ 16




Table of Contents continued

MVS -ii- Disk and Tape

5.3 Tape Library................................................................................................................ 17

5.3.1 Submitting Tapes ................................................................................................. 17

5.3.2 Retrieving Tapes .................................................................................................. 18

5.3.3 Academic Tape Retention Policy........................................................................ 19

5.4 Tape Library Management System (TLMS) ............................................................. 19

5.5 Backup Tapes .............................................................................................................. 20

5.6 JCL for Tape Data Sets............................................................................................... 20

5.6.1 DSN Parameter .................................................................................................... 21

5.6.2 Specifying Density ............................................................................................... 22

5.6.3 Using Multiple Data Sets on a Single Volume .................................................. 22

5.6.4 Preventing Extra Tape Mounts and Demounts................................................. 22

5.7 Creating a Sequential Tape Data Set......................................................................... 23

6. DISK ARCHIVING .......................................................................................................... 247. RACF AND MVS SECURITY ......................................................................................... 24

8. TAPE VOLUME SECURITY ........................................................................................... 25

8.1 RACF Tape Volume Protection ................................................................................. 25

8.2 TLMS Write Protection .............................................................................................. 26

8.2.1 SCRATCH Status ................................................................................................. 27

8.2.2 Request for Data Set Services Form ................................................................... 27

8.2.3 Protection Periods................................................................................................ 28

Appendix A .......................................................................................................................... 29

Appendix B........................................................................................................................... 32

Appendix C........................................................................................................................... 32



Instruction, Research & Infrastructure Support, Arizona State University

IBM Mainframe July 2002


MVS -1- Disk and Tape

1. INTRODUCTION

1.1 Abstract

This document discusses methods of storing information on the IBM MVS system. It

explains how data and programs are organized and stored in data sets on magnetic disk

and magnetic tape, and describes basic data set management tasks such as creating,

enlarging, and deleting files.

1.2 Update Information

Minor editing changes have been made. Disk quotas are no longer enforced. With the

exception of disk quotas, the previous version dated April 1998 is still valid.

2. DATA SET BASICS

2.1 ASCII and EBCDIC Character Sets

Computers store individual characters, such as letters and numbers, as a sequence of

bits. Unfortunately, the sequence of bits used to represent a specific character varies

from computer to computer.

The collection of all possible characters and their associated bit sequences is a character

set. The two most popular character sets are the American National Standard Code for

Information Interchange (ASCII) and the Extended Binary-Coded Decimal Interchange

Code (EBCDIC).

The IBM system uses the EBCDIC arrangement, while many other systems use the

ASCII arrangement. If you plan to transport a magnetic tape elsewhere, find outwhether the other computer requires ASCII or EBCDIC data, so you can write your tape

in the appropriate character set.





2.2 Blocking

Blocking is a technique for improving the execution speed of your programs at the

expense of added memory requirements. Disk and tape drives are mechanical devices

whose operation is much slower than electronic speed of data transfer. Hence, it is faster

to read or write records as a group (i.e., block) rather than individually.

Blocking is independent of the program; i.e., you don't have to change anything in your

program or change how you run your program. The program reads or writes one record

at a time, without any awareness of blocking.

More records can be stored in the same amount of space when records are blocked. On

both disk and tape, an inter-record gap appears between blocks; with unblocked data,

the gap appears between each record, Also, with larger blocks, there are fewer gaps in a

file.

There are both physical and practical limits for the size of a block. The system allows

you to control the size of a block. The term blocksize (or blksize) refers to the size of the

block in bytes. The term blocking factor refers to the number of records in a block.

These two terms are related but not interchangable. (For example, for a block containing

ten eighty-column records, the blocking factor is 10 and the blocksize is 800.)

2.3 Record Format

In general, the elements in a data collection vary in length. For example, a set of names

will likely contain short, medium, and long names. There are several ways of storing

elements as records in a data set. One method involves finding the length of the longest

data element and allowing every element in the set that number of bytes of storage

space. For example, if you had a list of names and the longest name was 42 bytes, you

would reserve 42 bytes on a storage device for each record.

This type of record format is called a fixed-length format because each record occupies

a fixed number of storage bytes, regardless of the actual length of the correspondingdata element. The space reserved for each record depends upon the length of the longest

data element in that data set. A disadvantage of the fixed-length format is that many

data elements may not require all of the allotted storage space, wasting bytes of space.

The variable-length record format solves this problem. The storage space that is alloted

to an individual record in this format depends only on that record's length, and not on

the length of any other record in that data set. On the IBM computer, a 4-byte field is





stored before every variable-length record, indicating the length of the record that

follows. There are no "wasted" bytes since the computer uses this 4-byte field to

determine the record's beginning and end.

The IBM computer also allows you to use an undefined-length format for records that

don't conform to the fixed or variable-length format. This format treats entire blocks as

units of data. That is, the computer won't separate blocks of data into individual

records. Programs that use this type of data must be able to extract records from blocks,

since this is not done by the operating system.

You may place both fixed and variable-length records in blocks, but a single block

cannot contain both record types. Each block of fixed-length records, with the possible

exception of the last block, has the same number of bytes. The last block is short if there

aren't enough records to fill it. Blocks of variable-length records vary in size. A 4-byte

field precedes each one in storage, containing the length of that block.

2.4 Data Sets

A data set is a collection of related records in one of several standard organizations.

People often refer to data sets as files. Although it will help you to understand about

bits, bytes, and records, much of your work on the IBM computer will involve data sets

There are several ways of organizing information within a data set. Depending on the

situation, one way may provide advantages such as more efficient storage and faster

retrieval of data than another type of organization. IBM refers to the different data set

organizations it supports as sequential, indexed sequential, direct access, and

partitioned. The two most common data sets at ASU are sequential and partitioned data

sets.

2.4.1 Sequential Data Sets

In a sequential data set , the computer stores and retrieves records in order. Forexample, it will always process the first and second records in a sequential data set

before it processes the third record. In addition, a sequential data set consists of a single

body of related records and doesn't contain subdivisions. These characteristics

distinguish sequential data sets from other data sets.





The records in a sequential data set may be either fixed or variable in length, and may be

grouped into blocks for efficiency. Sequential data sets may be stored on both disk and

magnetic tape.

One of the most common sequential data sets is the card-image data set. It consists of

80-column fixed and blocked records. Usually a card-image data set contains data or

programming code for a language such as FORTRAN, COBOL, or PASCAL. Some

programs on the IBM computer cannot read variable-length or undefined-length

records, but easily read the records in a card-image data set.

2.4.2 Partitioned Data Sets

A partitioned data set consists of partitions or members , each of which is similar to a

small sequential data set. There can be many members in a partitioned data set, andeach data set contains a directory for locating these individual members. When a

member is stored in a partitioned data set, its name and location are recorded in the

directory.

Partitioned data sets are handy for organizing a group of related programs or data.

They are also efficient for storing data that consists of 500 or fewer 80-column records.

Partitioned data sets are commonly used for storing source code libraries, procedure

libraries, and load module libraries. (A partitioned data set is also called a library.)

Whenever a partitioned data set member is removed or replaced, the portion of the data

set it originally occupied becomes unusable. To reclaim this wasted space, you must

condense or compress the data set. To do this, use the ISPF 3.4 compress utility. The

utility removes any "dead" space that may be distributed throughout a partitioned data

set, and add this amount to the pool of available space.

A partitioned data set is usually stored on magnetic disk, and can only be put on tape in

unloaded form. Because the unloaded form is a special format, members of a

partitioned data set stored on tape cannot be used directly by a program. The data set

must be restored (or loaded) back to disk before any of its members can be used.





3. MECHANICS OF DISK AND TAPE

3.1 External Storage Devices

The IBM computer runs programs and performs calculations within its large main

memory. Unfortunately, this memory is not large enough to hold all of the programs

and data that are submitted to it. Also, when the power to the system is turned off, the

computer loses all information in main memory. Because of these limitations,

mechanical devices called external storage devices were developed to store information

for later use.

Although these devices store and retrieve information slowly compared to main

memory, they offer larger storage capacities and the ability to retain information for

long periods of time, even after the computer system has been turned off. External

storage devices include magnetic disk, magnetic tape, magnetic drum, cards and papertape. Of these, magnetic disk and magnetic tape are used most often.

3.2 Disk Volumes

A magnetic disk drive (also called a disk volume or disk pack) contains a set of metal

platters that are stacked one atop another and placed on a spindle. The top and bottom

of each platter surface is coated with magnetic material that stores information, and a

set of read/write heads connected to an access arm floats just above and below the

surfaces of each of the spinning disk platters, transferring information to and from the

disk.

Disk is a direct-access storage method because the access arm positions the read/write

head directly over the desired information without reading other irrelevant data. This

distinguishes disk from sequential storage methods such as magnetic tape, where all

data preceding the desired information must first be read and discarded. Direct access

storage devices usually retrieve data faster than sequential storage devices.

3.2.1 Tracks, Cylinders, and Extents

The track is the most common unit of disk storage on the ASU IBM computer. Accounts

are granted in tracks, the size of a data set is displayed in tracks, and the system records

the total number of tracks allocated and in use for each account.





Tracks are concentric bands on the surface of a magnetic disk's platters. The amount of

information that may be stored on a track is measured in bytes, and different disk drives

have different capacities. At ASU, IBM 3380 disk drives are used for both permanent

and temporary storage of data sets. The table below displays some of the physical

characteristics of an IBM 3380 disk.

A group of vertically aligned tracks on a magnetic disk's platters is called a cylinder.

The number of tracks in a cylinder is fixed for a particular type of disk drive.

ASU Disk Drive Characteristics

(IBM 3380)

Bytes per track 47476

Tracks per cylinder 15

An extent is a group of contiguous (uninterrupted) tracks on a disk volume. Extents are

an important consideration when you supply primary and secondary space allocations

for a data set. The IBM computer's operating system will allow a data set only sixteen

extents per disk volume.

3.2.2 Volume Table of Contents

One particularly important data set called the Volume Table of Contents (VTOC)

appears on each disk volume and contains information about all the data sets on the

volume. The name, creation date, last reference date, starting and ending tracks, the

number of extents, and the record length of each data set is stored in the Volume Table

of Contents. The starting and ending tracks are recorded so that the read/write head of

the disk volume can locate the appropriate data set on the disk. When you work with a

data set, the entry for that data set in the VTOC is updated.

3.3 Tape Volumes

A magnetic tape is a long strip of magnetically sensitive material. The strip is wound

around a reel and encased in a plastic container. The tape must be physically mounted

on a tape drive before information can be stored on or retrieved from it. The tape drive





feeds the tape past a read/write head which actually rests on the tape, storing and

retrieving information from it. Tapes deteriorate when used frequently because of the

contact between the tape and the read/write head. This is one of several reasons you

should make backup copies of your.

Although the IBM computer provides security to prevent mounting the wrong tape, and

to prevent you or another person from accidentally writing over a tape volume, you

should know about a "built-in" protection feature called write protection. This is a tab

(or removable ring) found on most tapes. When the tab is set (or the ring removed), a

tape drive cannot write on the tape. If you have valuable information on your tape

and won't need to write on it, write-protect the tape before you check it into the tape

library.

Labels are the internal records on a tape which identify that volume and the data sets on

it. Most labeled tapes have a volume label and data set header and trailer labels. Thevolume label is used to assign a name to your tape volume. At ASU, the volume label

for academic users is a six-digit number that begins with the digits 18 or 8. Elsewhere,

volume labels may consist of letters as well as numbers. The volume label is written

before any other information on your tape.

Since there may be several files on one tape volume, header labels are written before

each data set on a labeled tape to identify the data set's name and characteristics. The

header labels on IBM standard label tapes include the creation and expiration date,

record format and length, and blocksize of each file. Data set trailer labels appear after

each data set on an IBM standard label tape and contain most of the same information

as the header label.

When you check a new tape into the ASU tape, you must decide whether your tape will

be labeled or not. Nonlabeled tapes contain no volume or data set labels; special

characters called tape marks separate each data set on a nonlabeled tape, but do not

provide any descriptive information about the tape. Tape marks are also used to

separate data sets on labeled tapes.





4. USING DISK

4.1 MVS Accounts

4.1.1 Account Types

An IBM MVS account allows you TSO and batch access. This means that you may use

the interactive facilities (TSO) and to run program on the batch system

4.1.2 Disk Space Accounting

Note: As of April 2002, disk quotas are no longer enforced. The information has been

left in this document for historical purposes.

Each person with an MVS account is assigned a fixed amount of disk space for storing

programs and data. This disk space quota is allocated in units of tracks and its value

varies depending on the type of account. To determine your disk space quota and the

amount of space your data sets are occupying, type the LISTUSER command. (If typing

the command on an ISPF command line, include the word TSO in front of the

command.)

LISTUSER userid

Several lines will be displayed on your screen. One line will begin with“INSTALLATION DATA” followed by “MAX” and “USED”. MAX is your disk quota

in tracks. Used is the number of tracks currently being used.

If you exceed your disk space quota, the system will prevent you from creating new

data.

The following suggestions should help you use your disk space more efficiently:

• Store small sets of similar data in a partitioned data set.• Use efficient blocksizes for your data sets.

• Move seldom used data sets to tape.

• Delete unnecessary data sets.

If you've followed these suggestions and still need more space, you may request a larger

disk space quota from the Computer Accounts Office.





4.2 Estimating the Size of a Data Set

To manage your account space efficiently, you need to know the approximate number

of tracks a disk data set will occupy. This allows you to judge how much information

can be stored within your disk space quota. This is useful, for example, if you receive

files on a magnetic tape, and need to know if you have enough space on your MVS

account to accomodate the data. If you can estimate disk space accurately, you can also

avoid the problems that occur when you've reached or exceeded your disk space quota.

You'll also be able to plan for growth, so that you can add more programs or data later.

When creating a new data set in a batch job, you must provide an estimate of the

number of tracks that data set will require. You specify this value in the JCL SPACE

parameter. If you use a value that's too low, the program will fail because your data

won't fit into the allotted space. If you provide too large a value, you'll waste your diskspace.

4.2.1Est imating Space for Card-Image Data

One of the most common data formats is the 80-column card-image. The following

table gives the number of tracks required for storing different numbers of 80-character

records, blocked at 7440 bytes per block.

Card-Image Disk Space Requirements

Number of Records Tracks Needed

50 1

500 1

1000 2

2000 4

5000 910000 18

25000 45





To calculate the exact amount of space needed for a data set with fixed block records,

see Appendix A. The formulas given there will work for any record length and

blocksize.

4.2.2 Estimating Space for Variable-Format Data

For variable-format data sets, there is no easy way to determine how much space you

will need. This is because trailing blanks are removed from each line by the editor before

storing the file. This saves considerable provided the lines do vary in length. There is a

4-byte overhead for each line in variable format which must be included in the space

estimate.

4.2.3 Estimating Space for SAS and SPSS Data Sets

Both SAS and SPSS can save your data in special formatted data sets. These data sets

contain your data and variable names, and may include other information such as data

formats, variable labels, and data set histories. SAS data sets in this format are called

SAS databases. SPSS formatted data sets are called SPSS system files. For information

on estimating the space required by a SAS database or a SPSS system file refer to the

SAS or SPSS documentation.

4.3 Choosing an Efficient Blocksize

Whenever you create a data, you must supply the data set's blocksize. Consequently you

need to understand some general principles for selecting an efficient blocksize.

If you have fixed-length records, the computer allows you to place any number of these

records together in a block. That is, you may use any blocksize that is a multiple of your

record length. For example, if you have 80-byte records, you could select blocksizes of

80, 160, 240, and so on. Because each block has a certain amount of "overhead"

associated with it, a data set stored with one blocksize may require significantly lessdisk space than that same data set stored with a different blocksize. (This "overhead"

consists of parity bytes, address bytes, and other information that a disk volume uses to

locate and check data.) Most people consider saving disk space the most important

factor in choosing a particular blocksize.





If you want to store 80-byte records in a new data set, use a blocksize of 7440 bytes.

If you wish to save fixed-length records that are not 80-bytes long, you may use the

largest multiple of the record length that is less than or equal to 7476, 15476, or 23476.

Blocksizes larger than 23476 result in substantial amounts of unusable disk space. A

track contains only whole blocks, not partial blocks. For example, a track can hold two

blocks of size 23476, but only one block of size 23477 or larger.

As long as your blocksize is a multiple of your record length, you can use any blocksize

less than IBM's maximum blocksize of 32760 bytes. However, you should be wary of

using very large blocks since they require large amounts of buffer space and tie up other

resources.

The following table displays recommended blocksizes for different types of data sets.

You may use this table with both permanent and temporary data sets. (Both permanentand temporary data sets reside on IBM 3380 disk volumes.)

Recommended Blocksizes for Different Data Sets

Type of Data Set Recommended Blocksize

80-byte "card-image" 7440

object code 3120

procedure libraries 3120

load modules 15476

direct access do not block

4.4 JCL for Disk Data Sets

Whenever you create or use an existing data set in a batch job, you must supply the IBM

computer with Job Control Language (JCL) describing that data set. The JCL data

definition statement (DD statement) allows you to do.

The following table shows the five components of a JCL DD statement for a disk data

set:





JCL DD Statement Parameters for a Disk Data Set

Parameter Meaning

DSN the data set nameDISP the disposition of the data setUNIT the device used for storing the data setSPACE the disk space allocated to the data setDCB the data control block

Two typical DD statements for creating data sets are shown below:

A DD statement for a sequential data set:

//NEWFILE DD DSN=WYL.AQ.ASU.NEWFILE,

// DISP=(NEW,CATLG,DELETE),

// UNIT=RESRCH,// SPACE=(TRK,(30,2),RLSE),

// DCB=(RECFM=FB,LRECL=80,BLKSIZE=7440)

A DD statement for a partitioned data set:

//NEWFILE DD DSN=WYL.AQ.ASU.NEWFILE,

// DISP=(NEW,CATLG,DELETE),// UNIT=RESRCH,

// SPACE=(TRK,(5,,5)),


The SPACE parameter is the only difference between the two DD statements above The

next two sections describe how to supply SPACE values for sequential and partitioned

data sets.

4.4.1 SPACE Parameter for Sequential Data Sets

The general form of the SPACE parameter for a sequential data set is:

SPACE=(TRK,( p,s),RLSE)





The value p represents the primary space allocation , and s represents the secondary

space allocation. The primary space allocation is the amount of space the operating

system provides initially for the data set. You should supply a value for p which is large

enough to hold all of your data.

If your data set needs more space than the primary allocation, the operating system

allocates this space in units determined by the secondary space allocation. That is, the

operating system will give your data set "s" additional units of space as needed, up to a

maximum of fifteen times. If this extra space is not available on a disk volume, however,

your program will fail.

Specify small secondary space allocations to increase the chances that a disk volume will

contain the necessary additional space. In general, 10% of the primary space allocation is

a good number for the secondary allocation. As an example, suppose you have

estimated that one of your data sets will occupy four tracks.You could use the following SPACE parameter:

SPACE=(TRK,(4,1),RLSE)

The "TRK" within the SPACE parameter indicates tracks. This means that space will be

allocated to your data set in units of tracks. You may also allocate space in cylinders and

blocks. You should include "RLSE" in the SPACE parameter for sequential data sets; this

instructs the operating system to release any unused space that has been allocated to the

data set.

Note that if a data set occupies any portion of a track, the entire track is reserved for

that data set. For example, if you write 10 complete tracks and then just start the

eleventh track, the system will record 11 tracks allocated.

4.4.2 SPACE Parameter for Partitioned Data Sets

The general form of the SPACE parameter for a partitioned data

set is:

SPACE=(TRK,( p,s,d))

As in the SPACE parameter for sequential data sets, p represents the primary space

allocation and s represents the secondary space allocation. Note that a third value

appears in the SPACE parameter for partitioned data sets. This value, d , represents

directory blocks. Each directory block is a 256-byte area on disk used for storing the





names (not the contents) of members within a partitioned data set. The number of

directory blocks only affects the number of member names you can have within a

partitioned data set, not the total space allowed for storing the contents of these

members.

For partitioned data sets, allocate 25% to 50% over the estimated amount needed for p ,

so that you can edit old members and add new ones. Make the secondary allocation in

small increments. You may assign directory blocks generously because they don't

require much disk space. (The space for directory blocks is taken out of the primary

space allocation p.) In general, allocate one directory block for every five members you

expect to have in your partitioned data set.

When you create a partitioned data set, it will occupy the entire primary space

allocation whether it is full or not. For example, the following SPACE parameter

SPACE=(TRK,(5,,5))

allocates all five tracks of the primary allocation from the time that the data set is

created until it is deleted, regardless of how full it is. In general, do not use the "RLSE"

parameter to release unused space in a partitioned data set; you will need extra space

for editing and creating new members.

4.5 Creating a Data Set

A data set may be created interactively (via ISPF option 3.2) or in a batch job. The

process for creating a sequential data set or a partitioned data set is identical except for

the amount of directory space. A sequential data set has no directory space; a

partitioned data set does. Directory space (also called directory blocks) is space reserved

within the data set to hold the names of members residing in the data set. Omit or

specify a value of zero for the number of directory blocks to create a sequential data set.

Specify a positive non-zero value for the number of directory blocks to create a

partitioned data set. Each directory block can hold five or more member names.

4.6 Condensing a Partitioned Data Set

To reclaim wasted space in a partitioned data set, use the ISPF 3.4 compress option. This

command will "squeeze" all of the wasted space from the partitioned data set.





Each time you edit members in a partitioned data set, wasted space is formed. Use the

compress option often if you do a lot of editing in a partitioned data set.

4.7 Making a Data Set Larger

It is not possible to directly make a data set larger. You need to create a new larger data

set with a different name, then copy the original data set to the new data set. After

verifying the copy completed successfully, you can delete the original data set set and

then rename the new one to the original name.

4.8 Making A Data Set Smaller

To make a data set smaller, use the following program. This program will work with both sequential and partitioned data sets. (Condense your partitioned data set before

running this program.)

// JOB

//STEP EXEC SAS

//DSET DD DSN=WYL.xx.yyy.name,DISP=OLDPROC RELEASE DDNAME=DSET TRACKS=trk;

//

In the program above, replace "name" with the name of your data set. Replace "trk" with

the number of tracks to remain in the data set at the end of the program. If your data setrequires more tracks than the value you've specified for "trk", the program will release

only the unused space.

5. USING TAPE

The most common use of tape is to bring data from elsewhere to ASU. The other use is

to place data from ASU on it, for which you need either a new tape or an existing tape

on which to write.

5.1 Obtaining a New Tape

To obtain a new tape on which to write data, contact the tape librarian. There will be no

cost unless the quantity of tapes requested is large.





When you request a new tape, you can request the tape be initialized with IBM standard

labels, ANSI standard labels, or no labels (non-labeled).

5.2 Tapes from Another Institution

Many ASU researchers receive tapes from another institution. These tapes, called

stranger tapes , often contain data or programs that have been sent from a colleague or a

data collection agency (such as the US Census Bureau). The information needed to

effectively use a tape from another institution can be divided into two parts: volume

information and data set information.

Volume information consists of attributes, such as density and parity, which apply to

the entire tape volume. Data set information consists of those attributes, such as record

length and record format, which apply to individual data sets. (There are often severalfiles on a tape.)

The following "TAPE SUMMARY TABLE" presents a series of questions about your

tape volume and the data sets it contains. If you can answer these questions, you'll find

it much easier to use your tape at ASU.

TAPE SUMMARY TABLE

Volume Attributes

• What volume serial number was assigned to the tape when it was checked into

the ASU tape library?

• Was the tape created with or without labels?

• How many files are on the tape?

Data Set Attributes (answer for each data set)

• What is the volume sequence number of the data set?

• If the tape is labeled, what data set name appears on the label preceding the dataset (the header label)?

• What is the record format, record length, and blocksize of the data set?

• Is the data set written in the ASCII or EBCDIC character set?

• What program or utility was used to place the data set on tape?

If the institution from which you receive a tape can provide the tape in a variety of

formats, the following is recommended.





Recommended Attributes for ASU

• 3480 cartridge tape (preferred); temporarily, a 9-track reel-to-reel dual density

(6250/1600 bpi) odd parity drive is also available

• EBCDIC character set (preferred) or ASCII character set

• non-labeled or IBM standard labeled; ANSI labeled is also usable

• fixed-length format (preferred) or IBM variable-length format

• preferred record length of 80 bytes; 32760 bytes is the maximum

• minimum blocksize is 18; maximum blocksize is 32760

5.3 Tape Library

Most of the tape volumes used on the IBM mainframe computers are stored in the tapelibrary. The tape librarian works in this office, checking tapes in and out, and providing

other services for tape owners. You must check your tape into the library before you can

use it on any of the computers.

The library is located in Engineering B-Wing Room ECB-130. Enter through the B-wing's

south door and turn into the first room on the left side of the hallway.

5.3.1 Submitting Tapes

When you check-in a tape, the librarian will ask you to complete a "Tape Volume

Control" form. This form identifies the owner of the tape, and provides the librarian

with enough information to prepare it for use. When you complete this form, the

librarian will give you a copy. Keep this copy with your tape records; you will need

it to check your tape out of the library.

The process of preparing a blank tape for use on the IBM computer is initialization.

When the librarian initializes a tape, all data on it is erased. If your tape contains

valuable information, specify on the "Tape Volume Control" form that the tapeshould not be initialized. No initialization requests will be taken over the phone.

When you have completed the "Tape Volume Control" form, the librarian will assign

your tape a six-digit volume serial number and write this number on your copy. Unless

you catalog your tape data sets, you must include this volume serial number in the JCL

for any of your programs that use the tape.





5.3.2 Retrieving Tapes

You may check out your tape on either a temporary or permanent basis. A temporary

check-out allows you to use the tape elsewhere on campus for a short period of time

and maintain the same volume serial number while the tape is out of the tape library. If

you request a temporary check-out to send your tape off-campus, you must provide the

tape librarian with written justification for maintaining the current volume serial

number.

If you check a tape out permanently , that tape's volume serial number will be assigned

to another tape owner after a period of one year. You will not be issued the same

volume serial number if you decide later to check the tape back into the library.

To check your tape out of the tape library:

• Bring your copy of the "Tape Volume Control Form" to the tape librarian.

• Fill out and sign all necessary forms supplied by the tape librarian.

NOTE: If you do decide to check your tape back into the library after it has been

permanently removed, follow these suggestions:

• Have the librarian initialize your tape again if you don't need any of the

previous data and would like to start writing new information on it.

If you do not do this, the internal volume label, which was written the first time your

tape was initialized, will not match the new volume serial number assigned to it.

That is, the new number on the gummed label outside of your tape, used by the

operators to find and mount the tape, will no longer match the internal label.

Because of this discrepancy, the operating system will not allow your tape to be

mounted if you call for it as standard labeled in your JCL.

• If you need to use the information on the tape, treat it as a "stranger" tape anddon't have it initialized again.

You may read from (or write to) a non-labeled stranger tape (use NL in the LABEL

field of your JCL). You may only read from a labeled stranger tape (use BLP in the

LABEL parameter).





5.3.3 Academic Tape Retention Policy

The academic tape library will only house actively used tape volumes. A tape volume

becomes inactive two years after its last use. Once a tape is deemed inactive, an effort

will be made to return the tape to its owner. After a period of time, unclaimed tapes will

be erased and discarded.

Owners of tapes that are required for long term research projects and have extended

periods of inactivity may request retention of such tapes for longer periods. The request

must include written justification for the extended retention.

For a complete description of Tape Retention Procedures, see Appendix C.

5.4 Tape Library Management System (TLMS)

The Tape Library Management System (TLMS) functions together with the IBM

operating system to protect tapes and monitor tape activity and inventory. The tape

librarian and computer operators use TLMS to keep track of and control many of the

tapes in the library.

When you check-in a tape, the librarian assigns it a volume serial number and enters this

number into a TLMS data file. Later when you read or write a data set on the tape,

TLMS automatically retains information about the data set and stores it in its volume

master catalog. TLMS stores the following volume and data set information:

Tape Status

Keep Date

Data Set Name

Creation Date and Time

Expiration Date

Jobname that created the data set

The value recorded by TLMS for Tape Status and Keep Date directly affect thesecurity of your tape.





5.5 Backup Tapes

Magnetic tape is a desirable storage medium because a large amount of data can be

stored in a small space. One inherent disadvantage, however, is that damage to a small

section of your tape can cause a large data loss.

Computer tapes are like the cassette tapes used in a car stereo; they wear out and

eventually break down. When a computer tape is placed on a tape drive, the read/write

head is in contact with the tape. This friction between the read/write head and the tape

causes wear. Tapes that are used often will also stretch, causing the loss of important

data. Tapes are so sensitive that even a small amount of dust can be detrimental.

Although rare, data on a magnetic tape can also be lost because of a computer

operator's error. ASU IBM computer operators mount and dismount many tapes in one

day. Potentially, an operator could mount the wrong tape, or make another mistake thatcould damage your tape.

To protect yourself against these and other mishaps, make a backup copy of each

important tape that you own. A backup tape is a duplicate copy that can be used if the

original tape is destroyed. You should store these backup tapes in a secure place outside

of the tape library, such as your home or office

5.6 JCL for Tape Data Sets

The JCL for creating and using tape data sets is similar to the disk data set JCL that was

described previously. The following table shows the six components of a JCL DD

statement for a tape data set:





JCL DD Statement Parameters for a Tape Data Set

Parameter Meaning

DSN the data set nameDISP the disposition of the data setUNIT the device used for storing the data setVOL the volume serial number(s)LABEL the data set sequence number and label typeDCB the data control block

The following sections describe some special JCL considerations for tape use.

5.6.1 DSN Parameter

Use the DSN parameter to specify the name of a data set on a labeled tape. If you are

using a standard label tape, the name you supply in the DSN parameter must match the

data set name on the internal label of the tape. The TAPEMAP program will list these

labels if you don't know what they are.

You must also supply a data set name when reading a stranger tape. These tapes contain

internal data set labels which usually don't conform to ASU naming conventions;

nevertheless, you may use these internal names in your programs as long as you use

BLP in the LABEL parameter of your tape DD.

Supply a meaningful data set name (DSN) for data sets on nonlabeled tapes even

though a nonlabeled tape doesn't contain internal data set labels. This name will be

recorded by TLMS and will appear on a MYTAPES listing. The following example DD

statement could be used in a program which reads a nonlabeled tape data set:

//NLTAPE DD DSN=WYL.xx.yyy.filename,// DISP=OLD,

// UNIT=TAPE6250,

// VOL=SER=800000,// LABEL=(1,NL,EXPDT=90365),






You must supply all of the information about the tape data set when it resides on a

nonlabeled tape. This is different from a standard label tape which contains much

information on the internal data set labels.

5.6.2 Specifying Density

Density is specified only for writing on a 9-track tape but not for writing on 3480

cartridges. There are two parameters related to tape density: UNIT and DCB DEN. Use

UNIT=TAPE6250 when using a 9-track tape. Use DCB=DEN=4 for writing to a 9-track

tape at 6250 density; use DCB=DEN=3 for 1600 bpi density.

5.6.3 Using Multiple Data Sets on a Single Volume

You can store more than one data set on a single tape volume by varying the sequence

number within the "LABEL" parameter of a tape DD statement. The sequence number

indicates the position of the data set on the tape. For example, the LABEL parameter

LABEL=(5,SL)

indicates the fifth data set on the tape volume.

You must write data sets on a tape sequentially. That is, if you have four data sets on a

tape, you cannot write to the sixth position; you must first write a data set at the fifthposition. In addition, all the data sets on a tape volume must be written at the same

density.

5.6.4 Preventing Extra Tape Mounts and Demounts

Occasionally, you will need to perform several tasks that use the same tape volume in

one batch job. For example, you might copy two disk data sets to tape. In this situation,

your batch job will have two jobsteps: the copy jobstep for the first data set and the

copy jobstep for the second data set.

Normally when you have several jobsteps that use a single tape, the computer operator

is forced to demount the tape after each step and mount it again for the following step.

If you have many jobsteps, this becomes tedious for the operator and time-consuming

for you. To avoid this problem, code RETAIN in the VOLUME parameter of your tape





DD statements. This will keep your tape mounted for the next jobstep. The following

program uses the RETAIN parameter:

// JOB

//STEP1 EXEC IEBGENER//SYSUT1 DD DSN=WYL.AT.ZZZ.DATA1,DISP=OLD

//SYSUT2 DD DSN=WYL.AT.ZZZ.TAPE.DATA1,// DISP=(NEW,CATLG,DELETE),

// UNIT=TAPE6250,

// VOL=(,RETAIN,SER=800000),// LABEL=(1,SL,EXPDT=90365)

/*//STEP2 EXEC IEBGENER

//SYSUT1 DD DSN=WYL.AT.ZZZ.DATA2,DISP=OLD//SYSUT2 DD DSN=WYL.AT.ZZZ.TAPE.DATA2,

// DISP=(NEW,CATLG,DELETE),

// UNIT=TAPE6250,// VOL=SER=800000,

// LABEL=(2,SL,EXPDT=90365)/*

//

This program copies two data sets to tape. The first step copies DATA1 to position 1 of

the tape, and the second step copies DATA2 to position 2. Note that the RETAIN

parameter appears in the first step and prevents the system from automatically

demounting the tape; the operator won't need to mount it again for STEP2. RETAIN is

not used on the DD statement in STEP2 because this is the last step in the job.

5.7 Creating a Sequential Tape Data Set

The following job creates a sequential tape data set and uses the IEBGENER utility to

store the information that follows the "SYSUT1" DD statement into it:

// JOB statement

//STEP EXEC IEBGENER//SYSUT2 DD DSN=WYL.xx.yyy.TAPEDATA,

// DISP=(NEW,CATLG,DELETE),// UNIT=TAPE6250,

// VOL=SER=8xxxxx,

// LABEL=(1,SL,EXPDT=90365),// DCB=(RECFM=FB,LRECL=80,BLKSIZE=7440,DEN=4)

//SYSUT1 DD *...one or more lines of data...

/*

//





NOTES:

• The "UNIT" parameter requests that the tape volume be mounted on a 1600/6250

bpi tape drive.

• The "VOL=SER=" parameter requests that the tape volume with the serial number

8xxxxx be mounted.

• The LABEL parameter describes the type of tape (whether it is standard labeled,

SL, or nonlabeled, NL), and also specifies which position to store the file. The "1"

indicates that this is the first file on the tape.

• The "EXPDT" parameter sets the date that the data set will expire to the 365th

day of 1990.

• The "DEN" subparameter in the "DCB" parameter indicates the density that the

data set is to be written at. "DEN=4" specifies a 6250 bpi density).

6. DISK ARCHIVING

Because of an increasing demand for MVS disk space, disk archiving began in June 1990.

The new disk archiving system copies infrequently used MVS disk files to tape and then

deletes these files from disk, freeing needed space.

The archiving program runs weekly, and all files which have not been accessed in the

prior 90 days will be archived. An archived file is automatically restored to disk when

you access it.

ISPF option 3.4 displays a list of all your cataloged data sets, including archived data

sets. If the volume serial number of a data set is listed as “ARCIVE”, it has been

archived.

7. RACF AND MVS SECURITY

In May 1989, the Resource Access Control Facility (RACF) replaced the previous MVS

security system. RACF is software which provides security for account access, disk datasets, and tape volumes.

RACF allows you to access a disk data set or a tape volume if you are the owner. If you

are not the owner, it checks a system data base to determine if you will be allowed

access. As the owner of a data set or a tape volume, you can use RACF (via ISPF option

9.R on TSO) to establish which userids will be permitted access and what type of access

they are allowed. Online help is available within the RACF utility.





8. TAPE VOLUME SECURITY

Many ASU researchers own tapes containing valuable information which cannot be

shared with others for various reasons. If you are in this position, you need to

understand how tape security works to prevent others from accessing your data.

When a tape volume is placed in the tape library, anyone is permitted to read or write

on it except when:

• the owner of the tape volume has defined the volume to RACF and specified which

userids are allowed access to the tape volume

• the tape management system TLMS prevents you or another from overwriting a tapedata set because that data set or one that follows on the tape volume is not expired

8.1 RACF Tape Volume Protection

If you, the owner of a tape volume, want to have the tape volume protected by RACF,

you should contact the tape librarian and request that the tape volume be defined or

added (the terms are synonymous) to RACF.

Once the tape volume has been defined to RACF, you can inform RACF what the UACC

(univeral access) code should be and which userids, if any, should be allowed access to

the tape volume. You do not need to tell RACF that your userid should be allowed

access; since your userid is the owning userid, it already has access. RACF provides

protection on a tape volume level, not a tape data set level. If you permit a userid to

have a certain type of access to a tape volume, the userid has that type of access to all

tape data sets on the volume.

When a userid attempts to access a tape volume which has been defined to RACF, the

system checks to see if the userid is the owner of the tape; if so, access is granted. If theuserid doesn't own the tape, the system checks to see if the userid is on the access list for

the tape and the type of access permitted. (It is possible for the owner of a tape to

designate that certain userids are allowed to read the tape and that other userids are

allowed to read and write.) If the userid is not in the access list, the system checks the

universal access code UACC to determine what, if any, access should be allowed.





The following types of access codes are possible:

NONE - no access allowed

READ - read access

UPDATE - read and write access

CONTROL - same as UPDATE

ALTER - read, write, and delete access

If a tape volume had a UACC code of NONE and no userids existed in the access list,

only the owner would have access to the tape.

If a tape volume had a UACC code of NONE and three userids existed in the access list

(one with access of READ and the other two with access of UPDATE), only the owner

and the three userids would have access to the tape. One of the userids would have

READ access, two would have UPDATE access, and the owner would have ALTERaccess.

If a tape volume had a UACC code of READ and no userids existed in the access list,

any userid would be permitted to read the tape, but only the owner would have any

additional access.

The tape volume protection provided by RACF is available for standard labeled

tapes, non-labeled tapes, and foreign labeled tapes; however, only standard labeled

tapes are protected from human error resulting from the operator mounting the

wrong tape volume.

8.2 TLMS Write Protection

The best way of preventing anyone from writing on your tape, either by accident or

deliberately, is to remove the write ring when you check it into the tape library. When

this ring has been removed, a tape drive cannot write on the tape. Consequently, you are

also prevented from writing on the tape until the ring has been replaced.

At ASU, the Tape Library Management System (TLMS) also offers write protection to

prevent you and others from overwriting your tape data sets. This protection works for

both standard label and nonlabeled tapes. The write protection offered to your tape

depends upon whether or not the tape is in "SCRATCH" status.





8.2.1 SCRATCH Status

The Tape Library Management System (TLMS) records a status for each tape volume

under its control and provides write protection based on this value. A tape's status

assumes one of two values:

• SCRATCH : Any of the data sets on the tape can be overwritten.

• NOT SCRATCH : None of the data sets on the tape can be overwritten.

When you check a new, blank tape into the Tape Library, it is placed in "SCRATCH"

status. This status changes to "NOT SCRATCH" as soon as you write on the tape. When

a tape that contains valuable information is submitted, the librarian places it in "NOT

SCRATCH" status.

For most tapes, TLMS bases the status on a date value called the keep date. A taperemains in "NOT SCRATCH" status until the keep date, and then it is placed in

"SCRATCH" status. The expiration dates you code in your JCL for tape data sets

establish the keep date and control the protection period of your tape.

You may control your tape's status in two ways:

• Complete the "Request for Data Set Services" form to change the status.

• Assign appropriate expiration dates in the JCL you use to write to tape.

8.2.2 Request for Data Set Services Form

A special "Request for Data Set Services" form is available from the tape librarian and

the computing site operators. This form permits the following tape services:

• Scratch Tape Volumes

You may place one or more volumes into "SCRATCH" status by completing thissection of the form. The tape librarian will change the TLMS status from "NOT

SCRATCH" to "SCRATCH". You will then be allowed to overwrite any data set

on the tape volume.

Caution: When a tape is put into "SCRATCH" status, either by the tape

librarian or by TLMS because its keep date has passed, TLMS uncatalogs all

the cataloged data sets residing on the tape. You will need to recatalog all





these data sets after you have completed the work that required you to place

the tape in "SCRATCH" status.

• Change Keep Date for Tape Volumes

You may change the keep date by completing this section of the form. This

allows you to extend the protection period of your tape.

Complete the appropriate section of the "Request for Data Set Services" form, and

submit it to the tape librarian. Any requests to change a data set's expiration date or

place a volume in "SCRATCH" status must be submitted in person and signed by the

tape's owner. No requests for these services will be taken over the phone.

8.2.3 Protection Periods

The protection period is the length of time before any data set on a tape volume can be

overwritten. This protection period extends until the keep date, and then the tape is

placed in "SCRATCH" status and any data set can be overwritten. The expiration dates

that you assign in your JCL LABEL statement when you create a tape data set affect the

keep date, and as a result, control the protection period. If you code expiration dates in

your JCL, your tape's protection period automatically extends until the highest

expiration date you've coded for any of the data sets. If you do not supply expiration

dates within your JCL DD statements, then the tape volume will be in "NOT

SCRATCH" for a default period of three days after you write the last data set.

There are two ways of specifying an expiration date within the LABEL parameter: the

EXPDT keyword and the RETPD keyword. The EXPDT keyword specifies an actual

expiration date in the form yyyy/ddd, where yyyy is a 4-digit year and ddd is a 3-digit

day (representing the number of days (001 to 366) into that year). For example, the

statement

// LABEL=(1,SL,EXPDT=2005/365)

assigns an expiration date of December 31, 2005 to the first data set on a standard label

tape. The following statement

// LABEL=(2,SL,EXPDT=2007/031)

assigns an expiration date of January 31, 2007 to the second data set on a standard label

tape.





If you use the LABEL statements above to write two data sets to tape, your tape would

be protected until the most distant (future) expiration date; you would not be able to

overwrite either data set until the latest date.

If you use EXPDT=1999/365 , the data set will never expire.

The RETPD keyword specifies a retention period. The retention period is the number of

days until the data set expires. The general form of the RETPD keyword is:

RETPD=nnnn

where nnnn represents the number of days. For example, to protect your tape data set

for one year, code the following LABEL statement:

// LABEL=(1,SL,RETPD=365)

To write a new data set onto the end of a tape volume that already has data written on

it, submit the tape with the write ring intact, and have the tape librarian put the tape

into "NOT SCRATCH" status. As soon as possible you must run a batch job that reads

the last data set on the tape volume. This job will provide the Tape Library Management

System with enough information to protect your tape from being overwritten.

Appendix A: Estimating Space for Fixed-Block Data Sets

The following steps describe how to calculate the number of tracks a data set will

occupy on disk. This procedure applies only to fixed block data sets. Before you use this

procedure, you will need to know three attributes of your data set: the number of

records in the data set, the record length, and the blocksize.

1) Calculate the value of an intermediate constant D.

D = (BLKSIZE + 12) / 32

All data on a IBM 3380 is written in 32-byte increments. The value D is the

number of 32-byte increments used by the data in each of your blocks. The

12 bytes included in the equation are used for error checking. Substitute

the blocksize you will be using for the variable BLKSIZE. You will also





need to round D up to the next higher integer before you use this value in

step 2.

2) Determine the number of blocks that will fit in a track.

BT = 1499 / (15 + D)

In this equation, BT is the number of blocks that will fit in one track.

Substitute the rounded value you calculated for D in step 1. Round BT to

the next lower integer before you substitute it in equation 3.

3) Determine the number of records that will fit in a track.

RT = (BLKSIZE / RECLEN) * BT

Substitute your blocksize for BLKSIZE and your record length for

RECLEN in this equation. You will always receive an integer when you

divide BLKSIZE by RECLEN because in a fixed block data set, the

blocksize is a multiple of the record length. You will also need to

substitute the value BT you calculated in step 2 for the variable BT. When

you calculate RT, you will know how many records (with a given record

length and blocksize) fit in one track.

4) Calculate the total number of tracks your data set will take.

T = RECORDS / RT

Substitute the number of records in your data set for RECORDS, and the

value you calculated for RT in step 3 into this equation. If the value you

calculate for T is a decimal value, you will need to round this value to the

next higher integer.

T is the number of tracks you will need to store your data set. Rememberthat this value depends upon the record length and blocksize of your data

set, as well as the number of records you have. You will need to use steps

1-4 to recalculate T if you have a data set with a different record length or

blocksize.





Rounding to the next higher integer,

T = 20 tracks

Note: The estimation procedure given in this section is accurate to one track; that

is, you may find that your data occupy one track more or one track less than

the estimate. This is because the IBM computer will write a short last block

if there aren't enough bytes to complete a full block at the blocksize you've

specified. When it writes a short block, it may be able to fit the short block

in the remaining unoccupied space in the last track.

Appendix B: Recommended Block Sizes

The following block sizes are recommended for common types of

data sets on 3380-type disk storage.

a) 80 character card-image data sets (assuming RECFM=FB is specified): 7440

bytes per block.

b) Object code records and user PROCLIBS: 3120 bytes per block. The linkage

editor and user PROCLIB facility allow a maximum of 3200 bytes;

however, 3120 makes more efficient use of disk space.

c) Load Modules (executable programs): 15476 bytes per block (full track)

d) Print-image (133-character) records: 7448 bytes per block for print files

saved on disk for later printing.

e) For direct access (FORTRAN DEFINE FILE or COBOL Relative) data sets,

do not block the records.

Appendix C: Tape Retention Procedures

1) A policy statement is given to a user when a tape is checked into the

library




2) Owners of inactive tapes will receive a letter notifying them that their

tapes have not been accessed for 2 years. The letter will be sent to the

address given on the Tape Volume Control form when the tape was

submitted to the library. A copy of the tape retention policy will be

included in this letter.

3) Inactive tapes will be placed in a holding area within the tape library for

six months. Inactive tapes can be accessed in the usual way without any

degradation of service.

At any time, a tape owner may notify the Manager of Central Site

Operations in Engineering A wing, first floor, to retain tapes in an inactive

status for longer periods by providing written justification for the longer

retention period.

4) If inactive tapes are not claimed or requested for use in a job during the six

month holding period, they subsequently will be removed to off-site

storage for 12 months.

5) If a letter notifying a tape owner of impending action on the disposition of

an inactive tape is returned with no known forwarding address, the tape

will be placed immediately in off-site storage.

6) Five months after the first notification, owners of inactive tapes will be

sent a second letter notifying them that if their tapes are not claimed or

requested for use in a job within 30 days, they will be placed in unsecured,

off-site storage and will be destroyed in 12 months.

Access to tapes taken off-site will be provided within 48 hours of the

request. A job requesting an off-site tape will ABEND (abnormally end)

with a message from the operator to rerun the job after 48 hours have

elapsed.

7) A third notification will be sent to owners of tapes that have been in off-site storage for 10 months.

8) After 12 months in off-site storage, if the owner has not claimed the tape it

will be erased and discarded or used for other purposes

Questions about this policy or about the status of your tapes should be directed to the

disk and tape fundamentals

Documents