6.4 Defect Management
(2) Alternate cylinder assignment
A defective sector is assigned to the spare sector in the alternate cylinder.
This processing is performed when the alternate assignment is specified in the FORMAT TRACK command or when the automatic alternate processing is performed at read error occurrence.
Figure 6.8 shows an example where (physical) sector 5 is detective on head 0 in cylinder 0.
Figure 6.8 Alternate cylinder assignment
2 alternate cylinders are provided for each head in zone 12 (inner side).
When an access request to physical sector 5 is specified, the device accesses the alternated sector in the alternate cylinder instead of sector 5. When an access request to sectors next to sector 5 is specified, the device seeks to cylinder 0, head 0, and continues the processing.
(3) Automatic alternate assignment
The device performs the automatic alternate assignment when ECC correction performance is increased during read error retry, a read error is recovered. Before automatic alternate assignment, the device performs rewriting the corrected data to the erred sector and rereading. If no error occurs at rereading, the automatic alternate assignment is not performed.
An unrecoverable write error occurs during write error retry, automatic alternate assignment is performed.
