A Scsi Devices; Scsi Guidelines; Using Scsiselect With Scsi Devices - HP xw4200 Service And Technical Reference Manual

SCSI Guidelines

When installing and operating SCSI devices, you must follow these guidelines:
A narrow (50-pin) SCSI controller allows you to daisy-chain up to seven additional SCSI devices.
Counting the controller, that amounts to eight total SCSI devices.
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.
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.
HP 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.
If multiple SCSI devices are used, split the devices between channels from multiple controllers for
optimum performance. Cable length for the second channel should not be longer than 12 meters.
If two controllers are used, each can 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 or an external cable adapter.
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 workstation to overheat.
All SCSI controllers require a unique SCSI ID (0–15) for each SCSI device installed. For more
information, see
68-pin SCSI controllers require a 12-meter, maximum-length twisted pair, LVD cable with built-in
terminator, maximum of 15 drives.
Every SCSI chain or circuit must be terminated (closed) at both ends. Some system boards have
both ends of the SCSI cable connected to, and terminated by, the system board. Termination can be
accomplished in one of several ways:
Use a cable with a built-in terminator.
Use a cable with a terminating resistor plug in the last connector.
Connect a SCSI device with its termination enabled into the last connector.
Connect an external SCSI device with its termination enabled to the external SCSI connector on
the rear panel of the workstation.
Turn on all external SCSI devices before turning on the power to the workstation. This enables the
SCSI controller to recognize the external devices.
Using SCSI Select with SCSI Devices
The Ultra160 and faster SCSI host adapters include the SCSI Select utility to configure the host adapter
and to run the SCSI disk utilities. To run the SCSI Select utility:
154 SCSI DEVICES
"Jumpers" on page 155.