3.3 Defect Management
(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 HDD 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).
•Automatic alternate block allocation at write operation
If AWRE flag in the MODE SELECT parameter permits the automatic alternate block allocation, the HDD executes two kinds of automatic alternate processing during WRITE command processing as described below:
Type 1 (Reassignment of Uncorrectable Read Error)
1)Commands to be applied
-WRITE
-WRITE EXTEND
-WRITE at executing WRITE AND VERIFY
2)Application requirements
When any of the above commands is issued to LBA registered in the uncorrectable error log of the READ command (LBA log of uncorrectable error while the READ command is executed), the AWRE processing is applied.
3)AWRE processing
The following processings are performed when the LBA matches the one in the uncorrectable error log:
a)Primary media check
-Creates an uncorrectable error pattern (invalid LBA pattern) in the position of the error LBA, repeats the primary media check up to three times. If the error still occurs after the check repeated three times, it is judged to be defective. Then, it performs the alternate processing.
b)Alternate processing
-Alternate media check
Writes the data that causes an unrecoverable error into the alternate block, and performs the media check.
(If the alternate block is a defective sector, the block is registered to the G list, another alternate block is allocated.)
c)SA and defect map update processing (on alternate side)
When an error occurs in the alternate processing, this WRITE command terminates with error. When the alternate processing normally terminates, the WRITE command is executed.