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14
5.2
Reliability and service
You can enhance the reliability of Cheetah 4LP 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 achieves an MTBF of 1,000,000 hours when operated in an environment that
ensures that the case temperatures specified in column 2 of Table 3 are not exceeded (see Section 6.4.1).
Short-term excursions up to the specification limits of the operating environment (given in Table 3, column 1)
will not affect MTBF performance. Continual or sustained operation at case temperatures above the values
shown in Table 3, column 2, may degrade product reliability.
The following expression defines MTBF:
MTBF per measurement 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 will have accumulated at least nine months of operation. Data will be calcu-
lated on a rolling average base for a minimum period of six months.
Drive failure means any stoppage or substandard performance caused by drive malfunction.
5.2.2
Preventive maintenance
No routine scheduled preventive maintenance is required.
5.2.3
Service life
The drive has a useful service life of five years. Depot repair or replacement of major parts is permitted during
the lifetime (see Section 5.2.4).
5.2.4
Service philosophy
Special equipment is required to repair the drive HDA. In order to achieve the above service life, repairs must
be performed only at a properly equipped and staffed service and repair facility. Troubleshooting and repair of
PCBs in the field is not recommended, because of the extensive diagnostic equipment required for effective
servicing. Also, there are no spare parts available for this drive. Drive warranty is voided if the HDA is opened.
5.2.5
Service tools
No special tools are required for site installation or recommended for site maintenance. Refer to Section 5.2.4.
The depot repair philosophy of the drive precludes the necessity for special tools. Field repair of the drive is not
practical since there are no user purchasable parts in the drive.
5.2.6
Hot plugging Cheetah 4LP disc drives
During power-up and power-down periods, the hot SCSI connect/disconnect capability on Cheetah 4LP SCSI
disc units will produce no glitches and/or any corruptions on an active SCSI bus.
Note.
It is the responsibility of the systems integrator to assure that no temperature, energy, voltage hazard,
or ESD potential is presented during the hot connect/disconnect operation.
1. All I/O processes for the SCSI device being inserted or removed shall be quiescent. All other SCSI devices
on the bus shall have receivers that conform to the SCSI-3 standard.
2. A device being inserted shall make its power ground and logic ground connection at least 1 millisecond
prior to the connection of any device connector contact to the bus. The ground connections shall be main-
tained during and after the connection of the device to the bus.
3. A device being removed shall maintain its power ground and logic ground prior to, during, and for at least 1
msec after the disconnection of any device connector contact from the bus.
Estimated power-on operating hours in the period
=
Number of drive failures in the period
Cheetah 4LP Product Manual, Rev. B
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