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A compressed file can be returned to its original uncompressed form by one of the Expansion Utilities. The entire data set is expanded. The expanded data set is identical to the one that existed before compression. Data integrity is ensured by comparing the check byte appended to each compressed record to a check byte calculated as each record is expanded.
The EXPAND Utility can only expand data sets compressed using a custom FDT. The EXPANDX Utility can only expand data sets compressed using Standard Tables or the string compression methods, Super Express, or Express. The SHRHCXPD Utility can only expand data sets compressed using a Hardware Compression dictionary.
The OUTFILE DD statement defines the uncompressed data set written by the Expansion Utilities. RECFM and LRECL must be the same as in the original uncompressed data set, but BLKSIZE may differ.
The Expansion Utilities assume default values for certain DCB parameters if they are not specified by the user. RECFM, LRECL, and BLKSIZE may be omitted in most cases. The Expansion Utilities report the same INFILE and OUTFILE information, as does the Compression Utility.
Note on Disaster Recovery: If the CA Compress Subsystem is unavailable the Expansion Utilities can be used to expand compressed data sets, thus making them accessible. Minor differences between subsystem and utility logic require caution. In particular, to expand physical sequential data sets compressed by the subsystem whose uncompressed format is variable-length, you must include an INSUBSYS DD DUMMY statement in the utility expansion step to process them correctly.
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