Chapter 4 Theory

Data Compression

3 Correction: Generating corrected data from syndromes.

The correction depends on the number and types of errors involved:

• For one known C1 codeword pair in error in a sub-data set (C2 codeword), the operation is performed by the ECC co-processor hardware.

• For two or more known C1 codeword pairs in error, the matrix is

 

 

computed by firmware and the correction is performed by

 

 

hardware.

 

 

• For one or more unknown C1 codeword pairs, syndromes are

 

 

generated by hardware, error location is computed by firmware,

 

 

the matrix is computed by firmware and the correction is

 

 

performed by hardware.

 

During a write operation, if the servo system detects an error that may

 

Servo-tracking

Faults

result in adjacent data tracks being over-written, the write operation is

 

 

aborted. The write operation will not continue until the correct servo

 

 

tracking is re-established.

Data Compression

Typical data streams of text, graphics, software code, or other forms of data contain repeated information of some sort, whether it is at the text level where you can readily recognize regular repetitions of a single word, or at the binary level where the repetitions are in bits or bytes. Although most data is unique and random, the binary level data exhibits patterns of various sizes that repeat with varying degrees of regularity.

Storage efficiency is increased if the redundancies or repetition in the data are removed before the data is recorded to tape. Data compression technology significantly reduces or eliminates redundancies in data before recording the information to tape. This increases the amount of data that can be stored on a finite medium and increases the overall storage efficiency of the system.

With data compression, the redundant information in a data stream is identified and represented by codewords or symbols, which allow the same data to be recorded in a fewer number of bits. These codewords or

LTO-3 Tape Drive User’s Guide

35

Page 49
Image 49
Quantum LTO-3 manual Data Compression, Servo-tracking, Faults