Fujitsu MHT2020AT Product Manual page 231

(3) Automatic alternating processing
This technology assigns a defective sector to a spare sector of an spare cylinder
for alternate assignment.
This device performs automatic alternating processing in the event of any of the
following errors.
Automatic alternating processing is attempted for read error recovery by
heightening the ECC correction capability while a read error retry is in
progress.
Before attempting automatic alternating processing, writing and reading of
already corrected data is repeated for the sector in which an error occurred.
If a read error does not occur during this reading operation, automatic
alternating processing is not performed.
If error recovery is not successful even if a write fault error retry is executed,
automatic alternating processing is performed.
Figure 6.6 shows an example where automatic alternating processing is applied to
sector (physical) 5 with cylinder 0 and head 0.
Sector (physical)
Cylinder 0
Head 0
Alternate cylinder 0
Head 0
Already
assigned
Notes:
1. The alternate cylinder is assigned to an inner cylinder in each zone.
2. When an access request for sector 5 is issued, the sector assigned for
alternating processing of the alternate cylinder must be accessed instead of
physical sector 5.
If an access request for sectors after sector 5 is issued, seek is executed to
cylinder 0, head 0 in order to continue processing.
Figure 6.6 Automatic alternating processing
C141-E192-01EN
Defec-
tive
sector
(Not used)
This is assigned to an unassigned sector.
6.3 Defect Processing
779 780
779 780
6-11