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The alternate block allocation is executed by the FORMAT UNIT command, the REASSIGN
BLOCKS command, or the automatic alternate block allocation. Refer to Subsection 5.3.2 “Auto
alternate block allocation processing” of the SCSI Logical Interface Specifications for details of
specifications on these commands. The logical data block is allocated to the next physically
continued sectors after the above sector slip treatment is made. On the other hand, the logical data
block is allocated to spare sectors which are not physically consecutive to the adjacent logical data
blocks. If a command which processes several logical data blocks is specified, the HDD processes
those blocks in ascending order of logical data block.
(1) Alternate block allocation during FORMAT UNIT command execution
When the FORMAT UNIT command is specified, the allocation of the alternate block to those
defective sectors included in the defect list (P, G, or D) is continued until all spare sectors in the
same cell are used up. When they are used up, unused spare sectors in the alternate cylinder are
allocated to the defective sectors that follows the sector by means of alternate sector treatment.
Figure 3.7 is examples of the alternate block allocation during the FORMAT UNIT command
execution.
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