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Barracuda 18FC Product Manual, Rev. B
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 inter-
val 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 firm-
ware keeps a running count of the number of times the error rate for each attribute is unacceptable. To accom-
plish 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 pre-
dictive 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.
5.3
Reliability and service
The reliability of Barracuda 18FC disc drives can be enhanced by ensuring that the drive receives adequate
cooling. This section provides recommended air-flow information, temperature measurements, and other infor-
mation, which you can use to enhance the service life of the drive.
5.3.1
Mean time between failure (MTBF)
The production disc drive achieves an MTBF of 1,000,000 hours when operated in an environment that
ensures the case temperates specified in Section 8.4.1 are not exceeded. Short-term excursions up to the
specification limits of the operating environment will not affect MTBF performance. Operating the drive at case
temperatures above these values will adversely affect the drive's ability to meet specifications. See section 6.4,
"Environmental limits" on page 21.
The following expression defines MTBF:
MTBF = Estimated power-on operating hours in the period
Estimated power-on operating hours means the estimated total power-on hours (POH) for all drives in service.
Drive failure means any stoppage or substandard performance caused by drive malfunction.
• 8,640 POH per year
• 250 average on/off cycles per year
• Read/seek/write operation during 20% of POH
• Operating at nominal voltages
Data is calculated on a rolling-average base for a minimum period of six months.
5.3.2
Field failure rate vs time
The expected field failure rate is listed below. Drive utilization will vary. An estimate range of utilization is:
• 720 POH per month
• 250 on/off cycles per year
• Read/seek/write operation 20% of POH
• System provides adequate cooling to ensure the case temperatures specified in Figures 8 and 9 are not
exceeded. Short term excursions up to the specification limits of the operating environment will not affect
MTBF performance.
Number of drive failures in the period
15
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