Product Features
XL500S
20
RELEASED 10/21/10 (WD CONFIDENTIAL)
2679-701211-A06
3.10.7
ATA Error Logging
ATA Error Logging provides an industry standard means to record error events and supporting
information that is then accessible by the host. The event record includes the exact command
that caused the failure, the response of the drive, the time of the event and information about
the four commands immediately prior to the errant command. Error Logging can reliably and
quickly determine whether a system problem is the result of a hard drive failure or other
component malfunction. Error Logging retains total error count for the life of the drive and
complete records for the last five errors.
3.10.8
Defect Management
Every WD drive undergoes factory-level intelligent burn in, which thoroughly tests for and
maps out defective sectors on the media before the drive leaves the manufacturing facility.
Following the factory tests, a primary defect list is created. The list contains the cylinder, head,
and sector numbers for all defects.
Defects managed at the factory are sector slipped. Grown defects that can occur in the field
are mapped out by relocation to spare sectors on the inner cylinders of the drive.
3.10.9
Automatic Defect Retirement
The automatic defect retirement feature automatically maps out defective sectors while
reading or writing. If a defective sector appears, the drive finds a spare sector.
The following item is specific to automatic defect retirement on writes (write auto-relocation):
Data is always written to disk (using automatic defect retirement if required) and no error
is reported.
The following item is specific to automatic defect retirement on reads (read auto-relocation):
When host retries are enabled, the drive will internally flag any unrecoverable errors
(DAMNF or ECC). This flagging allows subsequent write commands to this location to
relocate the sector only if the sector test fails.
3.10.10 Error Recovery Process
The drive has five means of error recovery:
ECC On-the-Fly
Preamp Thermal Asperity (TA) Compensation
Read/Write Retry Procedure
Extended Read Retry Procedure
ECC On-the-Fly – If an ECC error occurs, the drive attempts to correct it on-the-fly without
retries. Data can be corrected in this manner without performance penalty. The details of the
correction algorithm appear in the next section.
Preamp Thermal Asperity Compensation – A Thermal Asperity (TA) is a baseline shift in the
readback signal due to heating of the magnetoresistive stripe on the head as a result of
physical contact with the disk or a particle. The preamp circuit has the ability to detect and
compensate for thermal asperities. When an error cannot be corrected by ECC On-the-Fly,
another retry is performed, where the preamp with its thermal asperity detection feature
determines if the error is due to a thermal asperity. Once the preamp determines that the error
is due to thermal asperity, preamp compensation is enabled. If preamp compensation alone is
not enough to recover, then the channel performs a series of TA-specific recoveries.
Read/Write Retry Procedure – This retry procedure is used by all disk controller error types. If
the procedure succeeds in reading or writing the sector being tried, then recovery is complete
and the controller continues with the command. Each retry operation also checks for servo
