Directory space for partitioned data sets

To create a partitioned data set (PDS), request a primary quantity large enough to include space for a directory. A directory is an index used by the system to locate members in the partitioned data set. It consists of 256-byte records, each containing directory entries. There is one directory entry for each member. The third quantity in the SPACE parameter must specify how many records the directory is to contain.

The directory is written at the beginning of the primary space. It must fit in the first extent of the data set. Request enough directory space to allow for growth of the data set. You cannot lengthen the directory once the data set is created. If the directory runs out of space, you must recreate the data set.

With SMS, you can specify the number of records for the directory on the SPACE parameter without specifying any other subparameters. For example:

   //DD12  DD   DSNAME=PDS.EXMP,DATACLAS=DCLAS12,SPACE=(,(,,20)),
   //         DISP=(NEW,KEEP)

For a complete description of the directory, including details on member entries to enable you to compute how many records to request, see z/OS DFSMS Using Data Sets.

Directory space for partitioned data sets extended

The size of a PDSE grows dynamically. If you specify directory size on the SPACE parameter, SMS uses the size you specify only if you later convert the PDSE to a PDS.