HGST Ultrastar 7K4000 (SAS) Hard Disk Drive Specification
303
20.15.2 Recommendations for System Error Log
The system error log should contain information about the Drive error that will allow recovery actions. The system error logs
should contain all the error information returned in the sense data. At a minimum, the following information about each error
occurrence should be logged.
• Valid bit and error code (Sense byte 0)
• Sense Key (Sense byte 2)
• Information bytes (Sense bytes 3 through 6)
• Command specific information (Sense bytes 8 through 11)
• Additional Sense Code (Sense byte 12)
• Additional Sense Code Qualifier (Sense byte 13)
• Field Replaceable Unit (Sense byte 14)
• Sense Key Specific (Sense bytes 15, 16, and 17)
• Vender Unique error information (Sense bytes 20 through 23)
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 dam-
age 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)” on page 143) 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 (Sur-
face 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.
To Next Page
Loading...
Need help?
General
