Seagate Enterprise Capacity 3.5 HDD v7 SAS Product Manual, Rev. C
37
8.0
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 considerations (errors in
communications between the initiator and the drive). In addition, Seagate provides the following technologies used to increase data integrity and
drive reliability:
• Deferred Auto-Reallocation (see Section 8.4)
• Idle Read After Write (see Section 8.5)
The read error rates and specified storage capacities are not dependent on host (initiator) defect management routines.
8.1
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 information on the drive Error Recovery
philosophy is presented in the
SAS Interface Manual
.
8.2
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
SAS 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 recovery 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 12 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.
Table 4 equates the read and write retry count with the maximum possible recovery time for read and write recovery of individual LBAs. The times
given do not include time taken to perform reallocations. Reallocations are performed when the ARRE bit (for reads) or AWRE bit (for writes) is one,
the RC bit is zero, and the recovery time limit for the command has not yet been met. Time needed to perform reallocation is not counted against
the recovery time limit.
When the RC bit is one, reallocations are disabled even if the ARRE or AWRE bits are one. The drive will still perform data recovery actions within the
limits defined by the Read Retry Count, Write Retry Count, and Recovery Time Limit parameters. However, the drive does not report any
unrecovered errors.
