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6.3 Disk Drive Error Recovery Processing
C141-C013 383
If the error cannot be recovered from even when retry processing is executed the
specified number of times, the HDD terminates the command which is currently
being executed with a CHECK CONDITION status. The sense key in the sense
data at this time is "MEDIUM ERROR [=3]" and the ASC/ASCO indicates
"Mechanical positioning error [=15-01]" or "Positioning error detected by read of
medium [=15-02]."
(2) Write error
This error is caused by failure to detect a servo mark pattern or failure in
positioning at the target cylinder during on-track operation for the target sector. If
this error is detected, the HDD performs a retry.
If a write error occurs, the HDD repositions at the target cylinder and retries the
desired operation. If the error is not recovered, the HDD will repeat a retry
(repositioning) until the number of retries reaches the value specified for the
MODE select parameter "Write Retry Count."
If the error is not recovered despite the specified number of retries, the HDD will
terminate the command with CHECK CONDITION status. The sense data at this
time includes the sense key "MEDIUM ERROR [=3] and ASC/ASCQ
"Unrecovered write offtrack error [=0C-03].
(3) Read error in uncorrectable data
This error is a failure to detect the Sync Mark pattern during reading of data or an
ECC error for which correction processing is impossible. If this error is detected,
the HDD, after waiting one revolution of the disk media, tries reading again.
When the error is not recovered from, reading is retried repeatedly the number of
times specified in the MODE SELECT parameter ("Number of Retries during
Read" or "Number of Retries during Write").
In cases where correction is possible during execution of retry processing, the
processing procedure is according to "Correctable Data Read Error" in item (3).
If errors cannot be recovered from even after retry is executed the specified
number of times, the HDD terminates the command that is currently being
executed with a CHECK CONDITION status. The sense key in the sense data at
this time is "MEDIUM ERROR [=3]" and the ASC/ASCO indicates "Sync Mark
not found for data field [=13-00]" or "Unrecovered read error [=11-01]."
In this error retry processing, rereading accompanied by head offset processing is
performed.
(4) Correctable data read error
This error is a correctable ECC error when data are being read. Processing
methods when this error is detected differ depending on the values specified in the
EER flag and DCR flag in the MODE SELECT parameters.
If immediate correction of errors is permitted (DCR = 0, EER = 1), the HDD
immediately makes error corrections in the data buffer and sends the corrected
data to the INIT. Also, in the case of Verify processing, at the point when it