Quantum LTO-4 (Model B), Руководство пользователя

Страница: 55 / 98

Chapter 4 Theory
Data Compression
LTO-4 (Model B) Half-Height Tape Drive User’s Guide 39
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 subdata set (C2
codeword), the operation is performed by the ECC coprocessor
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.
Servo-tracking Faults
During a write operation, if the servo system detects an error that may
result in adjacent data tracks being overwritten, 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 that allow the