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5.1.3
Seek errors
A seek error is defined as a failure of the drive to position the heads to the addressed track. After detecting an
initial seek error, the drive automatically performs an error recovery process. If the error recovery process fails,
a seek positioning error (Error code = 15h or 02h) will be reported with a Hardware error (04h) in the Sense
Key. Recoverable seek errors are specified at Less than 10 errors in 10
(Sense Key = 04h) are classified as drive failures.
5.1.4
Interface errors
An interface error is defined as a failure of the receiver on a port to recover the data as transmitted by the
device port connected to the receiver. The error may be detected as a running disparity error, illegal code, loss
of word sync, or CRC error. The total error rate for a loop of devices is the sum of the individual device error
rates.
5.2
Reliability and service
You can enhance the reliability of Cheetah K15.4 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 provides recommended air-flow information.
5.2.1
Mean time between failure (MTBF)
The production disc drive achieves an MTBF of 1,400,000 hours when operated in an environment that
ensures the case temperatures specified in Section 6.4.1 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").
The MTBF target is specified as device power-on hours (POH) for all drives in service per failure.
The following expression defines MTBF:
MTBF per measurement period = Estimated power-on operating hours in the period
Estimated power-on operating hours means power-on hours per disc drive times the total number of disc
drives in service. Each disc drive must have accumulated at least nine months of operation. Data is 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
• Operating at nominal voltages
• System provides adequate cooling to ensure the case temperatures specified in Section 6.4.1 are not
exceeded.
Drive failure means any stoppage or failure to meet defined specifications 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
Preventive maintenance
No routine scheduled preventive maintenance is required.
18
8
Number of drive failures in the period
Cheetah 15K.4 FC Product Manual, Rev. C
seeks. Unrecoverable seek errors
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