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2-2 eXtremeRAID Installation Guide

SCSI Termination

Each end of a SCSI bus must be terminated to maintain proper voltage levels

for SCSI control and data signals. The device used for this purpose is called

a terminator, and it can be built into a controller, a SCSI peripheral device, or

it can be a plug placed on the connector at the very end of a SCSI bus.

The DAC1164P controller is equipped with automatic SCSI termination

circuitry. If the controller is at the end of a SCSI bus, it automatically enables

on-board termination. The controller can also detect whether single-ended

(SE) or low-voltage differential (LVD) termination is required, and can set

the on-board termination type as needed.

If all the SCSI devices on a channel are connected either to an internal

connector of a channel, or to an external connector of a channel, the end of

the SCSI bus farthest from the DAC1164P controller must have a terminator

installed. In this case, the controller automatically enables on-board

termination. See Figure 2-1 for examples of internal or external drive

configurations.

If some SCSI devices are connected to the internal connector of a channel,

and some are connected to the external connector of the same channel, the

two ends of the SCSI bus farthest from the controller must each be

terminated. In this case, the DAC1164P controller automatically disables on-

board termination. See Figure 2-1 for an example of an internal – external

drive configuration.

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Mylex eXtremeRAID Installation Guide Page 16