Alternate Block Allocation Processing - Fujitsu MAA3182SC Oem Manual

5.4

Alternate Block Allocation Processing

If errors on the disk media which cannot be recovered from are detected, or if a recoverable
error occurs repeatedly in the same data block, it is necessary for the INIT to allocate an
alternate block for the data block where the error occurred using the REASSIGN BLOCKS
command. The procedure for alternate block processing is shown below.
Note:
An attempt will be made to copy the contents of the data area of the logical data block
specified in the "Defect Data" list to the alternate block allocated by this command, but in
some cases, the data cannot be copied. Confirmation of the contents of data in the
allocated alternate block, saving of data before issuing this command and restoring of data
after executing this command are the responsibility of the INIT.
1) Verify data blocks in accordance with the procedure in Section 5.3 for data blocks where
error occur. When such a data block is judged to be normal, alternate block allocation
need not be implemented. In this case, rewrite the original data to that data block if
necessary. When the data block is judged to be defective, implement the processing in
item 2) and after.
2) Specify a logical block address for a data block which is judged to be defective and issue
the REASSIGN BLOCKS command.
3) If the REASSIGN BLOCKS command is terminated normally, verify that logical data
block according to the procedure in Section 5.3. If that data block is judged to be correct,
allocate an alternate block and terminate processing. When the data block is judged to be
defective, return to 2) and issue the REASSIGN BLOCKS command again, then try
reallocating another alternate block for that logical data block.
The alternate block allocation history (defect position information) is registered as an addition
to the defect list (G List). Therefore, when reinitializing the hard disk with the FORMAT
UNIT command (see item 5.2.2), if use of the G List is specified, defect processing can be
performed which reflects the operation results up to that time. Also, since "Alternate sector
processing" is applied in alternate block allocation in the REASSIGN BLOCKS command, the
physical connectivity of the logical data block positions on the disk media is destroyed, but by
reinitializing the disk, as long as the number of defective sectors in the cylinder does not
exceed the number of spare sectors per cylinder, the logical data blocks are relocated by sector
slip processing so that their physical connectivity is maintained.
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