Scsi Guidelines - HP Xw6200 - Workstation - 2 GB RAM Technical Reference Manual

Appendix A SCSI Devices

SCSI Guidelines

NOTE These systems support a mixed configuration of UATA/IDE and SCSI hard drives. In a mixed
configuration the UATA/IDE drive must be specified as the boot drive.
When installing and operating SCSI devices, you must follow these guidelines:
A narrow (50-pin) SCSI controller enables 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 enables 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 can 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 A and B for optimum performance. Cable
length for the second channel should not be longer than 18 inches.
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
can block the airflow and cause the workstation to overheat.
All SCSI controllers require a unique SCSI ID (0–15) for each SCSI device installed. Refer to the
section on page 153 for more information.
68-pin SCSI controllers require a 53 inch maximum length-twisted pair, LVD cable with built-in terminator,
maximum of five drives with a minimum driving spacing of 5.25 inches.
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.
"Jumpers"
SCSI GUIDELINES 151