Reliability And Service; Mean Time Between Failure (Mtbf) - Seagate Cheetah 18FC ST118202FC Product Manual

Cheetah 18FC Product Manual, Rev. C
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 Cheetah 18FC disc drives can be enhanced by ensuring that the drive receives adequate cool-
ing. This section provides recommended air-flow information, temperature measurements, and other informa-
tion, 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 for all drives in service. Drive
failure means any stoppage or substandard performance caused by drive malfunction.
MTBF is based on the following criteria:
• 8,760 power-on hours per year
• 250 average on/off cycles per year
• Read/seek/write operation during 20% of power-on hours
• Operating at nominal voltages
• Systems must provide adequate cooling to ensure that you don't exceed the case temperatures specified in
Figures 8 and 9. Short term excursions up to the specification limits of the operating environment will not
affect MTBF performance.
Data is calculated on a rolling-average base for a minimum period of six months.
A S.M.A.R.T. predictive failure indicates that the drive is deteriorating to an imminent failure and is considered
an MTBF hit.
Drive failure means any stoppage or substandard performance caused by drive malfunction.
Number of drive failures in the period
15