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SEAGATE 1200 SSD PRODUCT MANUAL, REV. A 18
5.3.4 S.M.A.R.T.
S.M.A.R.T. is an acronym for Self-Monitoring Analysis and Reporting Technology. This technology is intended to recognize
conditions that indicate imminent drive failure and is designed to provide sufficient warning of a failure to allow administrators
to back up the data before an actual failure occurs.
Note. The drive’s firmware monitors specific attributes for degradation over time but can’t predict instantaneous drive
failures.
Each monitored attribute has been selected to monitor a specific set of failure conditions in the operating performance of the
drive and the thresholds are optimized to minimize “false” and “failed” predictions.
Controlling S.M.A.R.T.
The operating mode of S.M.A.R.T. is controlled by the DEXCPT and PERF bits on the Informational Exceptions Control
mode page (1Ch). Use the DEXCPT bit to enable or disable the S.M.A.R.T. feature. Setting the DEXCPT bit disables all
S.M.A.R.T. functions. When enabled, S.M.A.R.T. collects on-line data as the drive performs normal read and write
operations. When the PERF bit is set, the drive is considered to be in “On-line Mode Only” and will not perform off-line
functions.
An application can measure off-line attributes and force the drive to save the data by using the REZERO UNIT command.
Forcing S.M.A.R.T. resets the timer so that the next scheduled interrupt is in one hour.
An application can interrogate the drive through the host to determine the time remaining before the next scheduled
measurement and data logging process occurs. To accomplish this, issue a LOG SENSE command to log page 0x3E. This
allows applications to control when S.M.A.R.T. interruptions occur. Forcing S.M.A.R.T. with the REZERO UNIT command
resets the timer.
Performance impact
S.M.A.R.T. attribute data is saved to the media so that the events that caused a predictive failure can be recreated. The drive
measures and saves parameters once every hour subject to an idle period on the drive interfaces. The process of measuring
off-line attribute data and saving data to the media is interruptible. The maximum on-line only processing delay is
summarized below
Reporting control
Reporting is controlled by the MRIE bits in the Informational Exceptions Control mode page (1Ch). Subject to the reporting
method. For example, if the MRIE is set to one, the firmware will issue to the host an 01-5D00 sense code. The FRU field
contains the type of predictive failure that occurred. The error code is preserved through bus resets and power cycles.
Determining rate
S.M.A.R.T. monitors the rate at which errors occur and signals a predictive failure if the rate of degraded errors increases to
an unacceptable level. To determine rate, error events are logged and compared to the number of total operations for a given
attribute. The interval defines the number of operations over which to measure the rate. The counter that keeps track of the
current number of operations is referred to as the Interval Counter.
S.M.A.R.T. measures error rates. All errors for each monitored attribute are recorded. A counter keeps track of the number of
errors for the current interval. This counter is referred to as the Failure Counter.
Error rate is the number of errors per operation. The algorithm that S.M.A.R.T. uses to record rates of error is to set
thresholds for the number of errors and appropriate interval. If the number of errors exceeds the threshold before the interval
expires, the error rate is considered to be unacceptable. If the number of errors does not exceed the threshold before the
interval expires, the error rate is considered to be acceptable. In either case, the interval and failure counters are reset and
the process starts over.
Table 1:
Maximum processing delay
Fully-enabled delay
DEXCPT = 0
S.M.A.R.T. delay times 75 ms