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4.
5.
4.2
4.2.1
For maximum compatibility with various vendors and models,
use only the ANSI "Mandatory" commands.
Program only the error Sense Keys into the driver code, not
the additional Sense Codes.
The driver code can make deci-
sions based only on the Sense Keys, such as retry or abort.
However, the Sense Codes should be displayed or printed, as
they can greatly enhance diagnosis of problems with the
drives while troubleshooting.
Errors and Media Defects
Errors
Q200 Series drives incorporate integrated media defect handling and
ECC capabilities that eliminate the requirement for user defect maps,
and for writing dedicated defect-mapping software.
This also reduces
test time during system integration.
A Q200 Series drive is capable
of detecting and compensating for any new defective sectors that may
be detected during the life of the drive.
Errors Defined
Any discrepancy between recorded data and recovered data is defined as
a data error.
Errors are either "soft"--those not readily repeatable,
or "hard"--those repeatable with high probability.
Soft errors are
generally related to the signal-to-noise ratio of the system, and
represent marginal conditions of the media, heads, and circuitry, or
even interference from other equipment.
Hard errors are most often
due to defects, pits, scratches, or thin spots in the media.
These
defective media areas can be detected and skipped (not used).
Error Correcting Code
The ECC is a byte-based Reed-Solomon (t
=
2) double burst correcting
code with an interleave of 3, resulting in a 96-bit ECC.
This code
allows correction of any sector having one burst of 17 bits incor-
rect, and detection of any sector having up to three bursts of 17 bits
incorrect.
If the errors begin on byte boundaries, the code corrects
or detects a full three bytes (24 bits) incorrect.
Further, it
detects many errors worse than stated with very high probability,
while the probability of misdetection is very low.
4-5
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