The number of bytes that you specify for BLKSIZE depends
on the device type, the record format for the data set and other programs
that will read or write the data set. The maximum value that you
can code is 2,147,483,648 (coded without the commas) or 2G. When
your program uses the data set, the OPEN function may impose a smaller
limit. The maximum allowed by OPEN is:
- 2,147,483,648 for dummy data sets. Note that you cannot actually
get a buffer that large.
- 2,147,483,647 for tape that does not have ISO/ANSI Version 3 or
Version 4 labels. When writing with BSAM and QSAM, the system imposes
a limit that depends on the tape subsystem model. Currently the maximum
for certain models is 256K. See z/OS DFSMS Using Data Sets for more details about block size limits for specific models.
OPEN allows EXCP programs to have higher limits that depend on the
hardware.
- 2048 for tape that has ISO/ANSI Version 3 labels, where the minimum
value for BLKSIZE is 18 bytes. To allow a block size greater than
2048, use installation exit routine IFG0193G, described in z/OS DFSMS Installation Exits.Version
4 labels do not have this restriction.
- 32,760 for DASD, ISO/ANSI Version 4 tape labels,
and other data sets.