Technical information

HGST Ultrastar C15K600 Hard Disk Drive Specification
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20.15.3
Data Recovery Procedure
Statistically, most data error activity is noise related and has nothing to do with defects in the media. It is wrong for
the system to assume that every data error reported occurred because of a defect in the media. It is also wrong for
the system to assume that every data error that occurred because of a media defect rendered the Drive unusable.
Recurring data error activity at the same physical location is an indication of a problem. The problem can be due to a
media defect or magnetic damage. A media defect is physical damage to the recording capability of the media while
magnetic damage is a defect in the bit pattern written to the media.
In both cases, the error can be corrected without replacing the unit. The physical sector may require relocation. The
Drive determines the need to reassign a sector. The Mode Select Page 1 option bit ARRE (See Section 18.10.3
"Mode Page 01 (Read/Write Error Recovery Parameters)”) set active allows the Drive to relocate recovered read
data errors. Non recovered data errors or the ARRE bit being inactive will have additional sense codes returned to
recommend reassignment of sectors.
The need to reassign a sector should be infrequent. Sites not meeting error rate criteria are removed from use during
SAT (Surface Analysis Test) in Drive manufacturing. With the exception of some early life SAT escapes (sites that
were marginally missed during SAT), reassigning defective sectors should be rare. Frequent sector reassignment
may be an (early) indication of another type of failure. Sector reassignments are monitored as part of the predictive
failure analysis. When a threshold is exceeded, the Drive will notify the initiator that a scheduled service action is
required.
Drive soft error rates are based on extraneous random faults that are not predictable. Media defects discovered after
the Drive completes manufacturing final test need to be relocated so that soft error rates are not influenced by
predictable known error sites. Failure of the system to properly relocate defective media sites can have a direct
influence on system throughput and drive error rates.
20.15.3.1
Reassign a Physical Sector
The Drive determines the need to reassign physical sectors based on error activity. Once a physical sector requires
reassignment, the Drive will reassign the physical sector.