Seagate Cheetah 15K, Руководство по эксплуатации продукта

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Cheetah 15K.7 SAS Product Manual, Rev. C 39
10.0 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:
• Background Media Scan (see Section 10.4)
• Media Pre-Scan (see Section 10.5)
• Deferred Auto-Reallocation (see Section 10.6)
• Idle Read After Write (see Section 10.7)
The read error rates and specified storage capacities are not dependent on host (initiator) defect management
routines.
10.1 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 .
10.2 Drive error recovery procedures
When an error occurs during drive operation, the drive, if programmed to do so, performs error recovery proce-
dures 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 sev-
eral 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 consists of 13 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.