Maxtor D540X-4K - Manual (Page 61)

Basic Principles of Operation
Maxtor D540X-4K 20.4/40.0/60.0/80.0 GB AT 5-13
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As disk drive areal densities increase, obtaining extremely low error rates requires a
new generation of sophisticated error correction codes. Maxtor D540X-4K hard disk
drive series implement 288-bit quadruple-burst Reed-Solomon error correction
techniques to reduce the uncorrectable read block error rate to less than one bit in 1
x 10
14
bits read.
When errors occur, an automatic retry, a double-burst, and a more rigorous
quadruple-burst correction algorithm enable the correction of any sector with four
bursts of four incorrect bytes each, or up to sixteen multiple random one-byte burst
errors. In addition to these advanced error correction capabilities, the drive uses an
additional cross-checking code and algorithm to double check the main ECC
correction. This greatly reduces the probability of a miscorrection.
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When a data error occurs, the Maxtor D540X-4K hard disk drives check to see if the
error is correctable using hardware on-the-fly ECC correction. If the error is
correctable using hardware on-the-fly ECC correction, the error is corrected via
hardware and the data is transferred to the host system. The hardware on-the-fly ECC
correction process is very quick and does not stop the disk transfer.
If the data is not correctable using hardware on-the-fly ECC correction, the sector is
re-read in an attempt to read the data correctly without applying firmware triple, or
quadruple-burst ECC correction. Before invoking the firmware triple, or quadruple-
burst ECC algorithm, the drive will always try to recover from an error by attempting
to re-read the data correctly. This strategy prevents invoking correction on non-
repeatable errors. Each time a sector in error is re-read a set of ECC syndromes is
computed. If all of the ECC syndrome values equal zero, and XC syndrome value
equals to 0 or 0FF, the data was read with no errors, and the sector is transferred to
the host system. If any of the syndrome values do not equal zero, an error has
occurred, the syndrome values are retained, and another re-read is invoked. If the
retry algorithm reaches the last step of the retry table, or the last pass through the retry
table, and the sector still has a data error, then the drive will apply firmware ECC
correction to recover the data.
0QVG Non-repeatable errors are usually related to the signal to noise ra-
tio of the system. They are not due to media defects.
If the automatic read reallocation feature is enabled, and the drive used firmware ECC
correction to recover the data, then the drive will perform a media test on the sector
to determine if the error was caused by a grown media defect. The media test consists
of writing and reading the sector four times. If any one of the writes or reads fails, or
if any read requires firmware ECC correction to recover the data, then the sector is
automatically reassigned.
0QVG The Maxtor D540X-4K AT drives are shipped from the factory
with the automatic read reallocation feature enabled so that any
new defective sectors can be easily and automatically reallocated
for the average AT end user.