8.0Defect and error management
Seagate continues to use innovative technologies to manage defects and errors. These technologies are designed to increase data integrity, perform drive
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 8.4)
•Media
•Deferred
•Idle Read After Write (see Section 8.7)
The read error rates and specified storage capacities are not dependent on host (initiator) defect management routines.
8.1Drive 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).
8.2Drive 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.
Cheetah 15K.5 SCSI Product Manual, Rev. J | 35 |
