If you are using the input data set with fixed-length, unblocked records as a basis for creating a new data set, a work area is required. The size of the work area is given by:

If you are reading only the data portion of fixed-length unblocked records or variable-length records, the work area is the same size as the record.

You can save processing time by adding fixed-length or variable-length records to a data set by using the MSWA (main storage work area) parameter of the DCB macro to provide a special work area for the operating system. The size of the work area (SMSW parameter in the DCB) must be large enough to contain a full track of data, the count fields of each block, and the work space for inserting the new record.

The size of the work area needed varies according to the record format and the device type. You can calculate it during execution using device-dependent information obtained with the TRKCALC macro, DEVTYPE macro, and data set information from the DSCB obtained with the OBTAIN macro. The TRKCALC, DEVTYPE and OBTAIN macros are discussed in z/OS DFSMSdfp Advanced Services.

Restriction: You can use the TRKCALC or DEVTYPE macro only if the index and prime areas are on devices of the same type or if the index area is on a device with a larger track capacity than the device containing the prime area.

If you do not need to maintain device independence, you can precalculate the size of the work area needed and specify it in the SMSW field of the DCB macro. The maximum value for SMSW is 65 535.