ABCs of z/OS System Programming Volume 3 - IBM Redbooks

Large format data sets
Large format data sets are sequential data sets that can grow beyond the size limit of 65 535
tracks (4369 cylinders) per volume that applies to other sequential data sets. Large format
data sets can be system-managed or not. They can be accessed using QSAM, BSAM, or
EXCP.
Large format data sets reduce the need to use multiple volumes for single data sets,
especially very large ones such as spool data sets, dumps, logs, and traces. Unlike
extended-format data sets, which also support greater than 65 535 tracks per volume, large
format data sets are compatible with EXCP and do not need to be SMS-managed.
You can allocate a large format data set using the DSNTYPE=LARGE parameter on the DD
statement, dynamic allocation (SVC 99), TSO/E ALLOCATE, or the access method services
ALLOCATE command.
Basic format data sets
Basic format data sets are sequential data sets that are specified as neither extended-format
nor large-format. Basic format data sets have a size limit of 65 535 tracks (4369 cylinders) per
volume. They can be system-managed or not, and can be accessed using QSAM, BSAM, or
EXCP.
You can allocate a basic format data set using the DSNTYPE=BASIC parameter on the DD
statement, dynamic allocation (SVC 99), TSO/E ALLOCATE, or the access method services
ALLOCATE command, or the data class. If no DSNTYPE value is specified from any of these
sources, then its default is BASIC.
Objects
Objects are named streams of bytes that have no specific format or record orientation. Use
the object access method (OAM) to store, access, and manage object data. You can use any
type of data in an object because OAM does not recognize the content, format, or structure of
the data. For example, an object can be a scanned image of a document, an engineering
drawing, or a digital video. OAM objects are stored either on DASD in a DB2® database, or
on an optical drive, or on an optical or tape storage volume.
The storage administrator assigns objects to object storage groups and object backup
storage groups. The object storage groups direct the objects to specific DASD, optical, or tape
devices, depending on their performance requirements. You can have one primary copy of an
object and up to two backup copies of an object. A Parallel Sysplex allows you to access
objects from all instances of OAM and from optical hardware within the sysplex.
z/OS UNIX files
z/OS UNIX System Services (z/OS UNIX) enables applications and even z/OS to access
UNIX files. Also UNIX applications also can access z/OS data sets. You can use the
hierarchical file system (HFS), z/OS Network File System (z/OS NFS), zSeries File System
(zFS), and temporary file system (TFS) with z/OS UNIX. You can use the BSAM, QSAM,
BPAM, and VSAM access methods to access data in UNIX files and directories. z/OS UNIX
files are byte-oriented, similar to objects.
Chapter 2. Data set basics 21