User Manual

Constellation.2 SAS Product Manual, Rev. K 49
9.0 Defect and error management
Seagate continues to use innovative technologies to manage defects and errors. These technologies are designed to
increase data integrity, perform drive self-maintenance, and validate proper drive operation.
SCSI defect and error management involves drive internal defect/error management and SAS system error consider-
ations (errors in communications between the initiator and the drive). In addition, Seagate provides the following
technologies used to increase data integrity and drive reliability:
• Background Media Scan (see Section 9.4)
• Media Pre-Scan (see Section 9.5)
• Deferred Auto-Reallocation (see Section 9.6)
• Idle Read After Write (see Section 9.7)
The read error rates and specified storage capacities are not dependent on host (initiator) defect management rou-
tines.
9.1 Drive internal defects/errors
During the initial drive format operation at the factory, media defects are identified, tagged as being unusable, and
their locations recorded on the drive primary defects list (referred to as the “P’ list and also as the ETF defect list). At
factory format time, these known defects are also reallocated, that is, reassigned to a new place on the medium and
the location listed in the defects reallocation table. The “P” list is not altered after factory formatting. Locations of
defects found and reallocated during error recovery procedures after drive shipment are listed in the “G” list (defects
growth list). The “P” and “G” lists may be referenced by the initiator using the Read Defect Data command.
Details of the SCSI commands supported by the drive are described in the SAS Interface Manual. Also, more informa-
tion on the drive Error Recovery philosophy is presented in the SAS Interface Manual.
9.2 Drive error recovery procedures
When an error occurs during drive operation, the drive, if programmed to do so, performs error recovery procedures
to attempt to recover the data. The error recovery procedures used depend on the options previously set in the Error
Recovery Parameters mode page. Error recovery and defect management may involve using several SCSI commands
described in the SCSI Interface Manual. The drive implements selectable error recovery time limits required in video
applications.
The error recovery scheme supported by the drive provides a way to control the total error recovery time for the entire
command in addition to controlling the recovery level for a single LBA. The total amount of time spent in error recov-
ery for a command can be limited using the Recovery Time Limit bytes in the Error Recovery mode page. The total
amount of time spent in error recovery for a single LBA can be limited using the Read Retry Count or Write Retry Count
bytes in the Error Recovery mode page.
The drive firmware error recovery algorithms consist of 20 levels for read recoveries and five levels for write. Each level
may consist of multiple steps, where a step is defined as a recovery function involving a single re-read or re-write
attempt. The maximum level used by the drive in LBA recovery is determined by the read and write retry counts.