Using CA Tape Encryption in Your z/OS Environment › Integrated Compression for Symmetric Key Encryption › Fundamental Data Compression Methods
Fundamental Data Compression Methods
The compression feature uses variations of the following fundamental data compression methods:
- Run Length Encoding data compression basically eliminates repeating characters. A string of repeating characters is replaced by the character and the number of times it is repeated.
- Huffman data compression is fundamentally the substitution of bit codes for data characters. The codes are constructed such that frequently occurring characters have very short codes while those occurring less frequently or rarely have codes that are longer than the character being replaced. The net overall storage required to store the data is typically less after code substitution.
- Adaptive Ziv-Lempel compression is actually an encoding process where the data is replaced by a stream of tokens. As each token is output a new code is generated and stored in a dictionary. As the encoding process continues, the new codes generated represent longer and longer strings. The encoding is done in such a way that the decoder can reconstruct the encoder's dictionary at expansion time. Thus, once the compression process completes, the dictionary is discarded. The dictionary is constructed above the bar to conserve 31-bit storage for the application environment.
- Hardware-assisted compression uses the IBM Hardware Compression facility, which uses Ziv-Lempel compression dictionaries.
The fastest compression algorithm provided is the S0 method. This algorithm is a run-length compression method that achieves good data compression with minimal CPU overhead.
CA Tape Encryption provides a utility, TBECMPCA, that accepts a disk or tape data set as input and compresses the data set with each of the supported compression algorithms. The utility then generates a report showing the fastest algorithm and the algorithm that provides the best compression ratio.
For more information about the available compression methods and the TBECMPCA utility, see the Configuration Guide.
