Seagate Cheetah 36LP ST336704LC, Product Manual

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14 Cheetah 36LP Product Manual, Rev. B
error (15h) is reported with a Medium error (3h) or Hardware error (4h) reported in the Sense Key. This is an
unrecoverable seek error. Unrecoverable seek errors are classified as failures for MTBF calculations. Refer to
the SCSI Interface Product Manual, part number 75789509, for Request Sense information.
5.2 Reliability and service
You can enhance the reliability of Cheetah 36LP disc drives by ensuring that the drive receives adequate cool-
ing. Section 6.0 provides temperature measurements and other information that may be used to enhance the
service life of the drive. Section 8.3.1 provides recommended air-flow information.
5.2.1 Mean time between failure
The production disc drive shall achieve an MTBF of 1,200,000 hours when operated in an environment that
ensures the case temperatures specified in Section 6.4.1, Table 3 are not exceeded. Short-term excursions up
to the specification limits of the operating environment will not affect MTBF performance. Continual or sus-
tained operation at case temperatures above the values shown in Table 3 may degrade product reliability.
The MTBF target is specified as device power-on hours (POH) for all drives in service per failure.
Estimated power-on operating hours in the period = MTBF per measurement period
Number of drive failures in the period
Estimated power-on operation hours means power-up hours per disc drive times the total number of disc drives
in service. Each disc drive shall have accumulated at least nine months of operation. Data shall be calculated
on a rolling average base for a minimum period of six months.
MTBF is based on the following assumptions:
• 8,760 power-on hours per year.
• 250 average on/off cycles per year.
• Operations at nominal voltages.
• Systems will provide adequate cooling to ensure the case temperatures specified in Section 6.4.1 are not
exceeded.
Drive failure means any stoppage or substandard performance caused by drive malfunction.
A S.M.A.R.T. predictive failure indicates that the drive is deteriorating to an imminent failure and is considered
an MTBF hit.
5.2.2 Field failure rate vs time
The expected field failure rate is listed below. Drive utilization will vary. An estimated range of utilization is:
• 720 power-on hours (POH) per month.
• 250 on/off cycles per year.
• Read/seek/write operation 90% of power-on hours.
• Systems will provide adequate cooling to ensure the case temperatures specified in Section 6.4.1 are not
exceeded.
Failure rate is calculated as follows:
• No system-induced failures are counted
• Based on 1,200,000 MTBF and 720 power-on hours per month
• Month 1’s rate includes a 300 PPM installation failure
Month 1 2,500 PPM
Month 2 1,650 PPM
Month 3 1,200 PPM
Month 4 1,000 PPM
Month 5 890 PPM
Month 6 840 PPM
Month 7 805 PPM