Fujitsu MAG3182FC SERIES Product Manual page 46

(3) Automatic alternate block allocation
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 EXTENDED command. This allocation
method is the same as with the REASSIGN BLOCKS command (alternate sector treatment).
Automatic alternate block allocation is made only once during the
execution of one command. If second defective block is detected,
the alternate block assignment processing for the first defective
block is executed but the alternate block assignment processing for
the second one is not executed and the command being executed
terminates. However, the initiator can recover the twice error by
issuing the same command again.
When an error is detected in a data block in the data area, recovery
data is rewritten and verified in automatic alternate block
allocation during the execution of the READ or READ EXTENDED
command. Alternate block allocation will not be made for the data
block if recovery is successful.
Example: Even if the data error which is recoverable by the
IMPORTANT
WRITE LONG command is simulated, automatic
alternate block allocation will not be made for the data
block.
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