Space is allocated for non-system-managed data sets or system-managed data sets without the guaranteed space attribute in the storage class as follows. If you allocate a new data set and specify SPACE=(TRK,(2,4)); this initially allocates two tracks for the data set. As each record is written to the data set and these two tracks are used up, the system automatically obtains four more tracks. When these four tracks are used, another four tracks are obtained. The same sequence is followed until the extent limit for the type of data set is reached.

• A sequential data set can have 16 extents on each volume.
• An extended-format sequential data set can have 123 extents per volume.
• A PDS can have 16 extents.
• A direct data set can have 16 extents on each volume.
• A non-system-managed VSAM data set can have up to 255 extents per component. System-managed VSAM data sets can have this limit removed if the associated data class has extent constraint removal specified.
• A system-managed VSAM data set can have up to 255 extents per stripe. This limit can be removed if the associated data class has extent constraint removal specified.
• A PDSE can have 123 extents.
• An HFS data set can have 123 extents on each volume.

You can allocate space for a multivolume data set the same as for a single volume data set. DASD space is initially allocated on the first volume only (exceptions are striped extended-format data sets and guaranteed space data sets). When the primary allocation of space is filled, space is allocated in secondary storage amounts (if specified). The extents can be allocated on other volumes. VIO space allocation is handled differently from other data sets. See Virtual I/O for Temporary Data Sets.