How it Works

Coding the SUBSYS parameter directs MVS to use the specified subsystem to process the data set. When you specify the CA Compress subsystem, it compresses and expands the data using I/O module ZSURSHRK, just as the Transparency does, so the results are completely compatible.

After the data is compressed, the SUBSYS parameter must be coded in order to access expanded data. If the data need not be expanded, for instance if it is simply being copied or sorted on an uncompressed field, there is no need to code the SUBSYS DD parameter to process the compressed data set.

Here is a simple example of the SUBSYS DD statement parameter:

//MYDDNAME DD DSN=MY.DATA.SET,DISP=OLD,
 // SUBSYS=(ZSAM,SHRK,SUPEREXP)

The string 'ZSAM' is the subsystem name given to the CA Compress subsystem by the systems programmer at your installation. The string 'SHRK' is a constant which must always be coded. The string 'SUPEREXP' is the name of the CA Compress compression algorithm that you want to use for this data set. When expanding a compressed data set you must specify the compression algorithm name used when the data set was originally compressed.