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7.1 Defect Management
C141-C013 391
c. Alternate block allocation processing
Alternate block allocation processing is implemented by the FORMAT UNIT
command, REASSIGN BLOCKS command or "Auto Alternate Block
Allocation Processing." In sector slip processing, the defective sectors re
excluded and logical data blocks are located in physically consecutive
sectors, but when alternate block processing is performed, the affected logical
data blocks are located in spare sectors which are not physically consecutive
with the previous and following logical data blocks which are physically
located on the disk.
− Alternate block allocation processing during FORMAT UNIT command
execution
With the FORMAT UNIT command, alternate block allocation is done
by sector slip processing until all the spare sectors within the same cell
have been used up for defective sectors included in the type of defect list
(P, G or D) specified in the command. When all the spare sectors in the
same cell have been used up, subsequent defective sectors in that cell are
treated by allocating spare sectors in an alternate cell by alternate sector
processing.
After implementing this alternate block allocation and initializing the
disk media, at times when a data block Verify (Certification) operation is
not prohibited, the HDD, reads all the initialized data blocks and verifies
their normalcy. If a defective data block is detected during this
processing, the HDD generates the C List as defect position information
and allocates alternate blocks by alternate sector processing for those
defective data blocks. In this case, alternate blocks are allocated in spare
sectors in an alternate cell.
− Alternate block allocation processing by the REASSIGN BLOCKS
command
With the REASSIGN BLOCKS command, alternate block allocation is
performed by alternate sector processing for defective logical data blocks
specified by the INIT. In this case, alternate blocks are allocated in spare
sectors in an alternate cell.
− Auto alternate block allocation processing
If auto alternate block allocation processing is permitted by the AWRE
flag or the ARRE flag of the MODE SELECT parameters, the HDD
executes alternate clock allocation automatically by alternate sector
processing for defective data blocks detected during execution of the
WRITE, WRITE EXTENDED, WRITE AND VERIFY, READ and
READ EXTENDED commands. The alternate block allocation method
in this case is the same as in the case of the REASSIGN BLOCKS
command. See the description in Section 6.3.2 concerning "Auto
Alternate Block Allocation Processing".