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3-14 C141-E185
(2) Alternate block allocation by REASSIGN BLOCKS command
When the REASSIGN BLOCKS command is specified, the alternate block is allocated to the
defective logical data block specified by the initiator by means of alternate sector treatment. If
there are unused spare sectors in the same cell as the specified defective logical data block, the
alternate block is allocated to these unused spare sectors. However, the alternate block is allocated
to unused spare sectors in the alternate cylinder when all spare sectors in the cell are used up.
Figure 3.8 is examples of the alternate block allocation by the REASSIGN BLOCKS command.
Alternate sectors
The same cell
Figure 3.8 Alternate block allocation by REASSIGN BLOCKS command
(3) Automatic alternate block allocation
• Automatic alternate block allocation at read operation
If the ARRE flag in the MODE SELECT parameter permits the automatic alternate block
allocation, the IDD automatically executes the alternate block allocation and data duplication on
the defective data block detected during the READ or READ EXTENDED command. This
allocation method is the same as with the REASSIGN BLOCKS command (alternate sector
treatment).
: Unused spare sector
: Defective sector
: n represents a logical data block number