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INTERFACE COMMANDS
7 – 14
S.M.A.R.T. Command Set
Execute S.M.A.R.T.
The Self-Monitoring Analysis and Reporting Technology (S.M.A.R.T.) command has been implemented to
improve the data integrity and data availability of hard disk drives. In some cases, a S.M.A.R.T. capable device
will predict an impending failure with sufficient time to allow users to backup their data and replace the
drive before data loss or loss of service.
The S.M.A.R.T. sub-commands (listed below) comprise the ATA S.M.A.R.T. feature set that provide access
to S.M.A.R.T. attribute values, attribute thresholds and other logging and reporting information.
Prior to writing a S.M.A.R.T. command to the device’s command register, key values must be written by the
host into the device’s Cylinder Low and Cylinder High registers, or the command will be aborted. For any
S.M.A.R.T. sub-command, if a device register is not specified as being written with a value by the host, then
the value in that register is undefined and will be ignored by the device. The key values are:
Key Register
4Fh Cylinder Low (1F4h)
C2h Cylinder High (1F5h)
The S.M.A.R.T. sub-commands use a single command code (B0h) and are differentiated from one another
by the value placed in the Features register. In order to issue a command, the host must write the sub-
command-specific code to the device’s Features register before writing the command code to the command
register. The sub-commands and their respective codes are:
D0h S.M.A.R.T. Read Attribute Value
This feature returns 512 bytes of attribute information to the host.
D1h S.M.A.R.T. Read Attribute Thresholds
This feature returns 512 bytes of warranty failure thresholds to the host.
D2h Enable/Disable Autosave
To enable this feature, set the sector count register to F1h (enable) or 0 (disable). Attribute values are
automatically saved to non-volatile storage on the device after five minutes of idle time and before
entering idle, sleep or standby modes. This feature is defaulted to “enabled” when S.M.A.R.T. is
enabled via the S.M.A.R.T. Enable Operations commands. The autosave feature will not impact host
system performance and does not need to be disabled.
D3h S.M.A.R.T. Save Attribute Value
This feature saves the current attribute values to non-volatile storage.
D4h Perform Off-Line Data Collection
Data is collected from random seeks, timed pattern seek times and head margin tests.
D8h Enable S.M.A.R.T.
D9h Disable S.M.A.R.T.
DAh S.M.A.R.T. Return Status
This feature allows the host to assess the status of a S.M.A.R.T. capable device by comparing all saved
attribute values with their corresponding warranty failure thresholds. If no thresholds are exceeded, the
drive is declared to have a positive health status. If any warranty failure threshold is exceeded, the drive
is declared to have a negative health status. Executing this sub-command results in all attribute values
being saved to non-volatile storage on the device.
DBh Enable/Disable Automatic Off-Line
To enable this feature, set the Sector Count register to F1h or 0 to disable.