Table 44 Rebuild Assist Log (15H) Data Structure Definition - Western Digital Ultrastar DC HC310 Specifications

9.17.5 Rebuild Assist
The Rebuild Assist mode provides a method for a host controlling the rebuild process to determine that logical
sectors on the failed device are unreadable without having to read every LBA to determine the unreadable logical
sectors (i.e., the read command is terminated with an error and the failed LBA is reported in the sense data).
The storage array controller then may reconstruct the failed logical sectors.
The remaining logical sectors may be copied to the replacement device.
If the Rebuild Assist feature is enabled, then the host should issue sequential READ FPDMA QUEUED commands
to extract the available data from the device.
If a READ FPDMA QUEUED command does not detect an unrecovered error, then the command should complete
without error.
The Rebuild Assist feature allows reporting of an unrecovered read error or an unrecovered write error that is either
predicted (i.e., a predicted unrecovered error) or unpredicted (i.e., an unpredicted unrecovered error).
If a device processes a READ FPDMA QUEUED command with the RARC bit set to one, then Rebuild Assist feature
shall not affect processing of the READ FPDMA QUEUED command.
If the device processes a READ FPDMA QUEUED command with the RARC bit cleared to zero and detects a
predicted unrecovered error, the following information recorded in the Queued Error log.
A) The Sense Key field is set to Bh(ABORTED COMMAND);
B) The Additional Sense Code field and the Additional Sense Code Qualifier field is set to 1103h
(MULTIPLE READ ERRORS);
C) The LBA field is set to the LBA of the first unrecovered logical sector; and
D) The Final LBA In Error field is set to the LBA of the last predicted unrecovered logical sector in a sequence of
contiguous unrecovered logical sectors that started with the first LBA in error.
9.17.5.1 Rebuild Assist log (15h)
If the device supports the Rebuild Assist feature (i.e., IDENTIFY DEVICE data Word 78 bit 11 is set to one), then the
Rebuild Assist log shall be supported.
Byte 7
0
1...6
7
8
(MSB)
7 + N
8 + N
(MSB)
7+(2×N)
8+(2×N)..511 Reserved

Table 44 Rebuild Assist log (15h) data structure definition

Physical Element Length
The Physical Element Length field indicates the number of bytes in the Disabled Physical Element Mask field and the
number of bytes in the Disabled Physical Elements field.
The device shall ignore any attempt by the host to change the value of this field when writing to the Rebuild Assist
log.
Disabled Physical Element Mask
The Disabled Physical Element Mask field indicates that bits in the Disabled Physical Elements field are supported.
The device shall ignore any attempt by the host to change the value of this field when writing to the Rebuild Assist
log.
6 5 4
Reserved
Reserved
Physical Element Length (N)
Disabled Physical Element Mask
Disabled Physical Elements
Western Digital Hard Disk Drive OEM Specification
3 2 1
73
0
Rebuild
Assist
Enabled
(LSB)
(LSB)