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Sense Data Error Recovery Methods
5 - 22 C141-E167
5.3 Disk Drive Error Recovery Processing
This section explains concerning error recovery processing methods and procedures executed by the
IDD for each type of disk drive related error. The INIT can control the error recovery processing
methods executed by the IDD using the MODE SELECT parameters.
5.3.1 Error states and retry processing procedures
(1) Seek error
Mechanical malfunctions of the disk drive during a seek operation and failure of serial addresses
detected during verification of the ID area to match are included in this error.
When a seek error occurs, the IDD first executes rezero seek, then tries repositioning at the target
cylinder and restarts the original processing. If the error is not recovered from, retry processing
(rezero seek and repositioning) is performed up to the number of times specified in "Number of
Retries during Seek Error" in the MODE SELECT parameters.
If the error cannot be recovered from even when retry processing is executed the specified number
of times, the IDD terminates the command which is currently being executed with a CHECK
CONDITION status. The sense key in the sense data at this time is "HARDWARE ERROR [=4]"
and the sense code indicates "Mechanical positioning error [=15-01]" or "Positioning error detected
by read of medium [=15-02]."
(2) Read error in uncorrectable data
This error is a failure to detect the Sync Byte pattern during reading of data or an ECC error for
which correction processing is impossible. If this error is detected, the IDD, 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 IDD 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 sense code indicates "Sync byte 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.
(3) 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 IDD 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 judges that correction is possible, it regards verification as
being successful and continues processing of subsequent data blocks.