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C141-E035-01EN 3 - 13
• Alternate sector treatment: The logical data block corresponding to defective sectors is
allocated to unused spare sectors in the same cylinder or unused spare sectors in the
alternate cylinder.
The alternate block allocation is executed by the FORMAT UNIT command, the REASSIGN
BLOCKS command, or the automatic alternate block allocation. Refer to OEM Manual–SCSI
Logical 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 IDD 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 specified lists (P, G, or D) is continued until all spare sectors
in the same cylinder are used up. When they are used up, unused spare sectors in the alternate
cylinder are allocated to the subsequent sectors in the cylinder by means of alternate sector
treatment. Figure 3.7 is examples of the alternate block allocation during the FORMAT UNIT
command execution.