Ultrastar 7K2
HGST Hard Disk Drive Technical Reference Manual
31
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 are 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.
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.
Error Recovery Process
The drive has five means of error recovery:
ECC On-the-Fly
Read/Write Retry Procedure
Extended Read Retry Procedure
ECC On-the-Fly – If an LDPC error occurs, the drive attempts to correct it on-the-fly without retries. Data
can be corrected in this manner without performance penalty.
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 errors. The procedure
ends when error recovery is achieved or when all possible retries have been attempted.
Extended Read Retry Procedure – This retry procedure tries combinations of positive/negative track offsets
and data DAC manipulations to recover the data. This retry procedure applies only to read data recovery.
The Read/Write Retry procedure performs the actual retry operation.
When an extended retry operation is successful, the controller continues with the command. The controller
clears any changes in track offset or data DAC settings before the command continues.
