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10.17 Rebuild Assist Feature Set
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.
See Section 12.21.11 for details on the Rebuild Assist Log 10.17.1 Enabling the Rebuild Assist Feature
If the host writes to the Rebuild Assist log and sets the Rebuild Assist Enabled field to one, then:
a) The device will initiate a self-test of the physical elements contained within the device and should disable any
physical elements that are not functioning correctly;
b) The device shall initialize the Disabled Physical Elements from the results of the self-test;
c) The device shall minimize device-initiated background activities; and
d) The device shall enable the Rebuild Assist feature. The host may verify that Rebuild Assist feature is enabled
by reading the Rebuild Assist log, and then examining the data returned and verifying that the Rebuild Assist
Enabled field is set to one
10.17.2
Using the Rebuild Assist Feature Overview
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.
10.17.3 Disabling the Rebuild Assist Feature
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 feature shall be disabled if:
a) The device processes a power cycle; or
b) The device processes a command to write to the Rebuild Assist log (see Section 12.21.11) with the Rebuild
Assist Enabled bit cleared to zero.
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Hard Disk Drive Specification