UPGRADING REPAIRING PCs

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Chapter 4—SCSI and IDE Hard Drives and Optical Drives
SCSI Configuration Troubleshooting
When you are installing a chain of devices on a single SCSI bus,
the installation can get complicated very quickly. Here are some
tips for getting your setup to function quickly and efficiently:
• Start by adding one device at a time—Rather than
plugging numerous peripherals into a single SCSI card and
then trying to configure them at the same time, start by
installing the host adapter and a single hard disk. Then, you
can continue installing devices one at a time, checking to
make sure that everything works before moving on.
• Keep good documentation—When you add a SCSI peripheral,
write down the SCSI ID address and any other switch and
jumper settings, such as SCSI Parity, Terminator Power, and
Delayed or Remote Start. For the host adapter, record the BIOS
addresses, IRQ, DMA channel, and I/O Port addresses used by
the adapter, and any other jumper or configuration settings
(such as termination) that might be important to know later.
• Use proper termination—Each end of the bus must be
terminated, preferably with active or Forced Perfect (FPT) terminators.
If you are using any Fast SCSI-2 device, you must
use active terminators rather than the cheaper, passive types.
Even with standard (slow) SCSI devices, active termination is
highly recommended. If you have only internal or external
devices on the bus, the host adapter and last device on the
chain should be terminated. If you have external and internal
devices on the chain, you generally will terminate the
first and last of these devices but not the SCSI host adapter
(which is in the middle of the bus).
• Use high-quality shielded SCSI cables—Make sure that
your cable connectors match your devices. Use high-quality
shielded cables and observe the SCSI bus-length limitations.
Use cables designed for SCSI use and, if possible, stick to the
same brand of cable throughout a single SCSI bus. Various
brands of cables have different impedance values, which
sometimes causes problems, especially in long or high-speed
SCSI implementations.
• Have the correct driver for your SCSI host adapter
and for each device—SCSI, unlike IDE, is not controlled
by your computer’s motherboard BIOS, but by software drivers.
A SCSI device cannot be used unless the appropriate
software drivers are installed for it. As with any other
software-driven peripheral, these drivers are often updated
periodically. Check for improved drivers and install them as
needed.