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SEAGATE ENTERPRISE PERFORMANCE 10K HDD V7 PRODUCT MANUAL, REV. C 14
Applications 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.
Applications 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 RTZ command resets the
timer.
Performance impact
S.M.A.R.T. attribute data is saved to the disk 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 disk is interruptable. 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 their 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.
Predictive failures
S.M.A.R.T. signals predictive failures when the drive is performing unacceptably for a period of time. The firmware keeps a
running count of the number of times the error rate for each attribute is unacceptable. To accomplish this, a counter is
incremented each time the error rate is unacceptable and decremented (not to exceed zero) whenever the error rate is
acceptable. If the counter continually increments such that it reaches the predictive threshold, a predictive failure is signaled.
This counter is referred to as the Failure History Counter. There is a separate Failure History Counter for each attribute.
Maximum processing delay
Fully-enabled delay
DEXCPT = 0
S.M.A.R.T. delay times 75 ms