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

2.6 Extended-format data sets and objects
An extended-format data set supports the following
options:
Compression
Data striping
Extended-addressability
Objects
Use object access method (OAM)
Storage administrator assigns objects
Figure 2-6 Types of extended-format data sets
Extended-format data sets
While sequential data sets have a maximum of 16 extents on each volume, extended-format
sequential data sets have a maximum of 123 extents on each volume. Each extended-format
sequential data set can have a maximum of 59 volumes, so an extended-format sequential
data set can have a maximum of 7257 extents (123 times 59).
An extended-format data set can occupy any number of tracks. On a volume that has more
than 65,535 tracks, a sequential data set cannot occupy more than 65,535 tracks.
An extended-format, striped sequential data set can contain up to 4 GB blocks. The maximum
size of each block is 32 760 bytes.
An extended-format data set supports the following additional functions:
► Compression, which reduces the space for storing data and improves I/O, caching, and
buffering performance.
► Data striping, which in a sequential processing environment distributes data for one data
set across multiple SMS-managed DASD volumes, improving I/O performance and
reducing the batch window. For example, a data set with 6 stripes is distributed originally
across 6 volumes.
Large data sets with high sequential I/O activity are the best candidates for striped data
sets. Data sets defined as extended-format sequential must be accessed using BSAM or
QSAM, and not EXCP (means no access method is used) or BDAM.
Chapter 2. Data set basics 25