A Scsi Devices; Scsi Guidelines - Compaq Evo W8000 Maintenance And Service Manual

SCSI Guidelines

When installing and operating SCSI devices, you must follow these guidelines:
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A narrow (50-pin) SCSI controller allows you to daisy-chain up to 7 additional SCSI
devices. Counting the controller, that amounts to 8 total SCSI devices.
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A wide (68-pin) SCSI controller allows you to daisy-chain up to 15 additional SCSI
devices. Counting the controller, that amounts to 16 total SCSI devices.
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If two narrow (50-pin) SCSI controllers are each connected to separate system board
SCSI connectors, each controller may have seven SCSI devices attached. Counting the
controller, this gives a total of 16 SCSI devices on the system.
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Compaq does not recommend mixing different width SCSI devices on the same SCSI
chain or on the same SCSI channel. Mixing devices of different widths on the same
chain or channel will always result in a data transfer rate of the slowest machine in that
chain. The only exception to this is that Ultra Wide SCSI devices will cause a speed
degradation when mixed with other 68-pin devices.
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If multiple SCSI devices are used, split the devices between Channels A and B for
optimum performance. Cable length for the second channel should not be longer than 18
inches.
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If two controllers are used, each may use SCSI devices having widths and speeds
different from the other. If a 68-pin data cable is used on a controller having 50-pin SCSI
devices, use an internal cable adapter (Compaq number 199618-001) or an external cable
adapter (Compaq number 270187-B21)
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CAUTION: Do not route data cables near the air intake to the power supply. Cables
routed in this manner may block the airflow and cause the computer to overheat.
All SCSI controllers require a unique SCSI ID (0-7 or 8-15) for each SCSI device installed.
The controller identifies a SCSI device by its SCSI ID number rather than its location.
Moving a SCSI device from one position to another on the SCSI chain does not affect
communication between the controller and the device. The reserved and available SCSI ID
numbers for SCSI devices are:
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0 is reserved for the primary hard drive.
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7 is reserved for the SCSI controller.
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1 through 6 and 8 through 15 are available for all other SCSI devices.
Maintenance & Service Guide
SCSI Devices
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