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10.4 SMART Feature Set
The intent of Self-monitoring, analysis and reporting technology (SMART) is to protect user data and prevent
unscheduled system downtime that may be caused by predictable degradation and/or fault of the device. By
monitoring and storing critical performance and calibration parameters, SMART devices employ sophisticated data
analysis algorithms to predict the likelihood of near-term degradation or fault condition. By alerting the host system of
a negative reliability status condition, the host system can warn the user of the impending risk of a data loss and
advise the user of appropriate action.
10.4.1
Attributes
Attributes are the specific performance or calibration parameters that are used in analyzing the status of the device.
Attributes are selected by the device manufacturer based on that attribute’s ability to contribute to the prediction of
degrading or faulty conditions for that particular device. The specific set of attributes being used and the identity of
these attributes is vendor specific and proprietary.
10.4.2
Attribute Values
Attribute values are used to represent the relative reliability of individual performance or calibration attributes. The
valid range of attribute values is from 1 to 253 decimal. Higher attribute values indicate that the analysis algorithms
being used by the device are predicting a lower probability of a degrading or faulty condition existing. Accordingly,
lower attribute values indicate that the analysis algorithms being used by the device are predicting a higher probability
of a degrading or faulty condition existing.
10.4.3
Attribute Thresholds
Each attribute value has a corresponding attribute threshold limit which is used for direct comparison to the attribute
value to indicate the existence of a degrading or faulty condition. The numerical values of the attribute thresholds are
determined by the device manufacturer through design and reliability testing and analysis. Each attribute threshold
represents the lowest limit to which its corresponding attribute value can be equal while still retaining a positive
reliability status. Attribute thresholds are set at the device manufacturer’s factory and cannot be changed in the field.
The valid range for attribute thresholds is from 1 through 253 decimal.
10.4.4
Threshold Exceeded Condition
If one or more attribute values, whose Pre-failure bit of their status flag is set, are less than or equal to their
corresponding attribute thresholds, then the device reliability status is negative, indicating an impending degrading or
faulty condition.
10.4.5
SMART Feature Set Commands
The SMART commands provide access to attribute values, attribute thresholds and other logging and reporting
information.
10.4.6
Off-line Read Scanning
The device provides the off-line read scanning feature with reallocation. This is the extension of the off-line data
collection capability. The device performs the entire read scan with reallocation for the marginal sectors to prevent
user data loss.
If interrupted by the host during the read scanning, the device services the host command. 10.4.7 Error Log
Logging of reported errors is supported. The device provides information on the last five errors that the device reported
as described in SMART error log sector. The device may also provide additional vendor specific information on these
reported errors. The error log is not disabled when SMART is disabled. Disabling SMART shall disable the delivering
of error log information via the SMART READ LOG SECTOR command.
If a device receives a firmware modification, all error log data is discarded and the device error count for the life of
the device is reset to zero.
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Hard Disk Drive Specification