(2)Alternate cylinder assignment
A defective sector is assigned to the spare sector in the alternate cylinder.
This processing is performed when a physical track contains three or more defective sectors, and when the automatic alternate processing is performed.
Figure 6.8 shows an example where (physical) sector 5 is detective on head 0 in cylinder 0.
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1 | 2 | 3 | 4 | 5 |
| 6 | 7 | 797 | 798 | |||
Cylinder 0 |
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Head 0 |
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1 | 2 | 3 | 4 | (unused) | 6 | 7 | 797 | 798 | ||||
Alternate |
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cylinder | Already |
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Head 0 | assigned |
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Defective sector is assigned to unassigned sector.
1 alternate cylinder is provided in inner side.
When an access request to 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.
Figure 6.8 Alternate cylinder assignment
(3)Automatic alternate assignment
The device performs the automatic assignment at following case.
1)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.
2)When a write error occurs and the error does not recovered.
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