Sense Data Error Recovery Methods
5.3Disk 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.
5.3.1Error 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
(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
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.
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