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Western Digital Hard Disk Drive OEM Specification
Disabled Physical Elements
The Disabled Physical Elements field specifies if physical elements shall be disabled. Each bit that is set to one in
the Disabled Physical Elements field specifies that LBAs associated with this physical element shall respond to read
commands and write commands as if the associated LBAs have predicted errors.
Each bit that is set to zero in the Disabled Physical Elements field specifies that LBAs associated with this physical
element shall respond to read commands and write commands as if the associated LBAs do not have predicted
errors.
9.17.5.2
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
9.17.5.3
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.
9.17.5.4
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 13.7.8) with the Rebuild Assist Enabled
bit cleared to zero.
9.17.6
Power Disable
The Power Disable feature is optional. If supported and enabled, the Power Disable feature may be used to disable
power to the device circuitry which enables a system that supports this feature to perform a hard reset of the drive.
When deploying drives in systems that do not support this feature, it is recommended that you select part
numbers without this option.
