110
9. If necessary, install the device’s drivers and configure the device according to the vendor’s
instructions.
Adding External SCSI Devices
You can add single-ended SCSI devices to the system by connecting them to the SCSI port on the back
of the base unit. Additional SCSI option boards (adapters) can be installed to support external SCSI
devices as well. Refer to the “Adding Option Boards” section to install new boards.
Understanding Cable Lengths
InterServe 650, 660 and StudioZ RAX systems are equipped with an Ultra SCSI controller (AIC 7860)
for all internal and external SCSI devices. By default, the controller arbitrates with each device (that is,
initiates sync negotiation) to determine the data rate the device will use to transfer data (5, 10, or 20
MHz). If the target device complies with the 20 MHz SCSI specification, then the data transfer rate
will be 20 MHz. If another device complies with 10 MHz, then date transfer will be at 10 MHz without
changing any settings for the controller or the target device.
The number of devices and length of the cables used to connect the devices becomes a factor when
using Fast SCSI-2 or Ultra SCSI devices. Ultra-SCSI devices impose shorter cable restrictions than
Fast SCSI-2 or SCSI-1. The total length of the SCSI cabling must not exceed the following:
Number of Devices
SCSI-1 Fast SCSI-2 Ultra SCSI
1 to 4 19.8 feet (6 meters) 9.9 feet (3 meters) 9.9 feet (3 meters)
5 to 7 9.9 feet (3 meters) 9.9 feet (3 meters) 4.9 feet (1.5 meters)
NOTE The SCSI controller (integrated or on an option board) counts as one device.
NOTE The AIC 7860 can be configured to transfer data at Fast SCSI-2 rates for all devices. This allows Ultra
SCSI devices to be installed without being hampered by the Ultra SCSI cable restrictions. Total cable
length can then be extended to the Fast SCSI-2 length. See “Disabling Sync Negotiation” on page 111
to configure the controller.
The total length of the SCSI cabling is the sum of the following:
u
SCSI bus trace length on I/O expansion board - 12.0 inches (30.5 cm)
u
SCSI cable inside the base unit - 3.8 feet (1 m)
u
SCSI cable inside each device (average) - 8 inches, (20 cm)
u
SCSI cable between the base unit and the first device
u
SCSI cable between each device
To Next Page
Loading...