Large format sequential data sets

A large format sequential data set is a modification to traditional sequential data sets that allows for more than 65535 tracks of data per volume. Large format sequential data sets can be single or multivolume, and can reside on SMS managed or non-SMS managed direct access storage devices.

A large format sequential data set is specified using the DSNTYPE=LARGE keyword on a JCL DD statement or using the dynamic allocation equivalent. z/OS XL C/C++ does not support the allocation of a large format sequential data set using fopen() or freopen().

z/OS XL C/C++ provides complete read and write support for:

Large format sequential data sets when seek is requested (not specifying the noseek keyword).
Large format sequential data sets when noseek is requested and honored. See Access method selection for more information on when noseek is requested but not honored.

Note: Restrictions associated with traditional sequential single and multivolume data sets, or concatenations of such data sets, continue to apply when the data set is large format.