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6.4 Alternate Block Allocation Processing
C141-E167 6 - 7
(3) Reading and verification of data
Issue the READ, READ EXTENDED or VERIFY command and verify that the data written to the
disk media in item (2) were read correctly.
To verify reading of data, it is recommended that reading of the same data block be done at lease 2
times, but the number of times verification is performed is determined by the conditions on the
system. If reading of all data is completed normally, it can be recognized that use of that data block
can be used normally.
(4) Error verification
When an error related to the disk media (Sense Key = 3: MEDIUM ERROR) occurs during writing
of the data pattern (see item (2)) or verification of data reading (see item (3)), reexecute the rewriting
and reading verification combination (two times) at least 8 times.
When the same type of error occurs even once during reexecution, it is recommended that the INIT
treat that data block as a defective block. If the reexecution of verification is completed normally
every time, it should be regarded that that data block can be used normally.
6.4 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 6.3 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 6.3. 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.