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Data Format
36 C141-E252
3.3 Defect Management
3.3.1 Defect list
Information of the defect location on the disk is managed by the defect list. The following are defect
lists which the HDDs manage.
• P list (Primary defect list): This list consists of defect location information available at the HDD
shipment and is recorded in a system space. The defects in this list are permanent, so the initiator
must execute the alternate block allocation using this list when initializing the disk.
• D list (Data defect list): This list consists of defect location information specified in a FORMAT
UNIT command by the initiator at the initialization of the disk. This information is recorded in
the system space of the HDD as the G list. To execute the alternate block allocation, the
FORMAT UNIT command must be specified.
• G list (Growth defect list): This list consists of defective logical data block location information
specified in a REASSIGN BLOCKS command by the initiator, information on defective logical
data blocks assigned alternate blocks by means of the HDD automatic alternate block allocation,
and information specified as the D list. They are recorded in the system space on the HDD.
The initiator can read out the contents of the P and G lists by the READ DEFECT DATA command.
3.3.2 Alternate block allocation
The alternate data block is allocated to a defective data block (= sectors) in defective sector units by
means of the defect management method inside the HDDs. The initiator can access all logical data
blocks in the user space, as long as there is no error.
Spare sectors to which alternate blocks are allocated can be provided in "alternate cylinders". See
Subsection 3.1.2 for details.
Both of the following are applicable to the alternate block allocation.
• Sector slip treatment: Defective sectors are skipped and the logical data block corresponding to
those sectors is allocated to the next physical sectors. This treatment is made on the same cell as
the defective sector's and is effective until all spare sectors in that cell are used up.
• Alternate sector treatment: The logical data block corresponding to defective sectors is allocated
to 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 Subsection 6.3.2 "Auto
alternate block allocation processing" of the SAS INTERFACE MANUAL 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.