OS/390 MVS IPCS User's Guid

v
v
Unformatted information in virtual storage access method (VSAM) data sets or
other types of data sets
Active system storage for the IPCS user’s address space
See OS/390 MVS Diagnosis: Tools and Service Aids for more information about
dumps and traces.
When you first access a source, IPCS recognizes the type of data in the source
and begins the appropriate type of processing.
Dump Data Set Processing
IPCS decides if the source data set should be treated as a system dump by
comparing the data set to the following criteria:
v
v
v
The dump data must be stored on a data set with sequential (PS), direct (DA), or
unidentified (*) organization.
The logical record length (LRECL) must be 4160 bytes
The data set must have one of the following combinations of record format
(RECFM) and block size (BLKSIZE):
RECFM=F,BLKSIZE=4160
RECFM=FB,BLKSIZE=4160
RECFM=FBS,BLKSIZE=n*4160 where n=1,2,...
If the data set meets these criteria, IPCS provides dump processing, meaning that
IPCS simulates system services, such as dynamic address translation and control
block formatting, when processing the source.
In systems with Data Facility Storage Management Subsystem/MVS (DFSMS/MVS),
IPCS supports extended sequential data sets, which IBM recommends using.
Extended sequential data sets:
v Have a greater capacity than sequential data sets
v Support striping
v Support compression
Some dump data sets are quite large compared with other data sets generated by a
system. The capacity of an extended sequential data set is enough to hold the
largest stand-alone dumps, as much as 128 gigabytes.
Striping spreads sections, or stripes, of a data set across multiple volumes and
uses independent paths, if available, to those volumes. The multiple volumes and
independent paths accelerate sequential reading and writing of the data set,
reducing the time during which dump and trace I/O competes with production I/O.
In a striped data set, when the last volume receives a stripe, the next stripes are
placed on the first volume, the second volume, the third, and so on to the last
volume, then back to the first volume. If n volumes are used, striping allows
sequential access to the data set at nearly n times the rate at which a single
volume data set can be processed. The faster processing speeds up moving dump
data from relatively expensive data space storage to less expensive DASD.
Compression allows dump data sets to use less DASD space. Before using
compression, consider the following:
v
Compression and decompression trade off processing cycles for more efficient
use of DASD. If software compression is used because hardware compression is
not available, the number of processing cycles is significantly higher and
noticeably impacts response time.
Chapter 1. Introduction to IPCS 5