Seagate ST118202LC, Product Manual

Page: 24 / 84

14 Cheetah 18 Product Manual, Rev. B
unrecoverable seek error. Unrecoverable seek errors are classified as failures for MTBF calculations. Refer to
Section 5.1.1.2 of the
SCSI Interface Product Manual,
part number 77738479, for Request Sense information.
5.2 Reliability and service
You can enhance the reliability of Cheetah 18 disc drives by ensuring that the drive receives adequate cooling.
Section 6.0 provides temperature measurements and other information that may be used to enhance the ser-
vice 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 1,000,000 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.
• Read/seek/write operation 20% of power-on hours.
• 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 20% 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
• PPM targets include 30% no defect found and handling failures
• Based on 1,000,000 MTBF and 720 power-on hours per month
• Month 1’s rate includes a 300 PPM installation failure
Month 1 2,364 PPM
Month 2 1,422 PPM
Month 3 1,403 PPM
Month 4 1,391 PPM
Month 5 1,317 PPM
Month 6 1,255 PPM
Month 7 1,162 PPM
Month 8+ 1,025 PPM