Data Compression Considerations - Quantum LTO-4 (Model B) User Manual

Chapter 4 Theory
Data Compression
Data Compression
Considerations
40
same data to be recorded in a fewer number of bits. These codewords
or symbols point back to the original data string, using fewer characters
to represent the strings. Because these smaller symbols are substituted
for the longer strings of data, more data can be stored in the same
physical space.
Some important benefits result from data compression in tape drives:
• The same amount of information can be stored on a smaller length
of tape.
• More data can be stored on a given length of tape.
• Performance can more closely parallel to that of high-transfer-rate
computers.
• More information can be transferred in the same time interval.
In an effective data-compression method, several factors are important:
• The amount of compression, which is measured by the compression
ratio. This ratio compares the amount of uncompressed data to the
amount of compressed data. It is obtained by dividing the size of
the uncompressed data by the size of the compressed data.
• The speed with which data is compressed and decompressed
relative to the host transfer rate.
• The types of data to be compressed.
• The data integrity of the compressed data.
The amount of compression possible in a data stream depends on
factors such as:
• Data pattern
• Compression algorithm
• Pattern repetition length
• Pattern repetition frequency
• Object size (block of information to be compressed)
• Starting pattern chosen
The transfer rate depends on factors such as:
• Compression ratio
LTO-4 (Model B) Half-Height Tape Drive User's Guide