Western Digital Purple PR1000M, Technical Reference Manual

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PR1000M
P
RODUCT
F
EATURES
2679-800020-A03 RELEASED 5/8/17 (WD CONFIDENTIAL) 19
The test may be run to completion or be performed as a background task as the drive
processes other commands from the host. The host may then poll the drive for
runtime status and test results. Since the test is embedded in the drive’s firmware, it
is always available, requires no installation and can be faster and more effective than a
software-based drive test.
3.15.7 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.
3.15.8 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.
3.16 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.
3.16.1 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.