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 like 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 don't 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.

Related reading: For more information on large format data sets, see z/OS DFSMS Using Data Sets.