Defect And Error Management; Drive Internal Defects; Drive Error Recovery Procedures - Seagate ST3146855LC - Cheetah 146.8 GB Hard Drive Product Manual

7.0

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 SCSI 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 7.4)
• Media Pre-Scan (see Section 7.5)
• Deferred Auto-Reallocation (see Section 7.6)
• Idle Read After Write (see Section 7.7)
The read error rates and specified storage capacities are not dependent on host (initiator) defect management
routines.
7.1

Drive internal defects

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 (see the SCSI Commands Reference Manual).
7.2

Drive error recovery procedures

Whenever 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 previ-
ously set up in the error recovery parameters mode page. Error recovery and defect management may involve
the use of several SCSI commands, the details of which are described in the SCSI Interface Product Manual.
The drive implements selectable error recovery time limits such as are required in video applications. For addi-
tional information on this, refer to the Error Recovery Page table in the SCSI Commands Reference Manual,
which describes the Mode Select/Mode Sense Error Recovery parameters.
The error recovery scheme supported by the drive provides a means 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 via 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 via the Read Retry
Count or Write Retry Count bytes in the Error Recovery Mode Page.
The drive firmware error recovery algorithms consist of 11 levels for read recoveries and 5 levels for writes.
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