Transcript A+ Guide to Managing and Maintaining Your PC, 5e

A+ Guide to Managing
and Maintaining Your PC
Fifth Edition
Chapter 22
All About SCSI
You Will Learn…

About basics of SCSI technology and
components

How SCSI hard drives compare to IDE drives

How to install a SCSI device

Troubleshooting tips for SCSI
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SCSI Basics


Standard for communication between
subsystem of peripheral devices and system
bus

Bus can contain/be used by up to 7 or 15 devices

Bus requires controller embedded on motherboard
or host adapter inserted into an expansion slot
Faster, more expensive, more difficult to install
than similar IDE devices

Mostly used in corporate settings
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The SCSI Subsystem

Enables two devices on SCSI bus to pass data
between them without going through CPU

Requires SCSI controller and unique SCSI IDs
assigned to each device, including host adapter

Components

Host adapters

Device drivers
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SCSI Host Adapter
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IDE versus SCSI Bus
Communication
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Host Adapters

Manage all devices on SCSI bus

Support internal and external SCSI devices

Form a single daisy chain with devices
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Considerations When Selecting
a Host Adapter

BIOS

Expansion slot

Bus mastering

SCAM-compliant
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BIOS Considerations

Plug and Play compatibility

Built-in configuration utility

Software that configures termination
automatically and assigns system resources

Ability to configure SCSI devices using the
bus controlled by the adapter

Support for up to 15 peripherals
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Expansion Slot Considerations

Host adapter must fit expansion slot
(eg, 16-bit ISA, PCI)
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Bus Mastering

Bus master attached to PCI bus can access
memory and other devices without accessing
the CPU

SCSI host adapter does not require a DMA
channel
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SCAM-Compliant

Can assign SCSI IDs dynamically at startup

Two levels


Level 1 requires that the devices – but not the host
adapter – be assigned an ID at startup by software
Level 2 requires that the host adapter – as well as
the devices – be assigned an ID at startup by
software
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SCSI Device Drivers

Enable OS to communicate with a host adapter

Two popular types


ASPI (Advanced SCSI Programming Interface) –
more popular of the two
CAM (Common Access Method)
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Variations in SCSI

Bus width

Signaling methods used on SCSI cables

Connectors used with SCSI cables

Termination

SCSI-1, SCSI-2, and SCSI-3
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Bus Width


Narrow SCSI

8-bit data path

Uses a cable with a 50-pin connector (A cable)
Wide SCSI

16-bit data path

Uses a cable with a 68-pin connector (P cable)
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Signaling Methods Used on
SCSI Cables
Single-ended (SE)
Differential
Send signal on pair of
twisted wires – one carries
voltage, one is a ground
 Less expensive than
differential
 Shorter maximum cable
length; data integrity is not
as great


Send signal on pair of
twisted wires – both carry
voltage; signal calculated to
be the difference between
the two
 Better signal accuracy and
greater reliability
 HVD and LVD
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Signaling Methods Used on
SCSI Cables (continued)
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SCSI Cables
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Signaling Symbols
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Connectors Used with SCSI
Cables

Not affected by signaling method used

Types vary in shape and pin density; can be
connected with adapters

Two main types:


50-pin (A cable)

68-pin (P cable)
Last connector on last device must be filled
with a terminator
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SCSI Connectors
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Multiple Connectors on the
SCSI Bus
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Termination

Prevents echo effect from electrical noise and
reflected data at end of SCSI daisy chain

Required at each end of a SCSI chain
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Ways to Terminate the End of a
SCSI Chain

Switch setting on host adapter that activates or
deactivates a terminating resistor on the card

Single SCSI connection or two connections

Resistor physically mounted on the device

Internal terminators that turn on or off with a
jumper setting on the device

Software-controlled termination
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External SCSI Terminator
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Terminators

Types

Passive terminators

Active terminators

Forced perfect terminators (FPTs)

Single-ended SCSI cables use passive
terminators, active terminators, and FPTs

Differential cables use either HVD or LVD
terminators
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Major Versions of SCSI

SCSI-1 (Regular SCSI)




No common command set
8-bit data bus
7 possible devices
SCSI-2 (Fast SCSI)




Common command set
16-bit data bus
15 possible devices
Mandatory parity checking
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Major Versions of SCSI
(continued)

SCSI-3 (Ultra SCSI)

Supports both parallel and serial data transmission

Supports FireWire connections

Data transfer of 320 MB/sec

Includes SPI standard
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SCIS Standards
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SCIS Standards (continued)
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SCIS Standard Cable Specs
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Comparing IDE and SCSI

IDE


May give better performance when using a single
disk drive with an OS like Windows 98 or
Windows Me
SCSI



Increases performance where heavy load is placed
on system and its components
Some OSs include increased support for SCSI
features and take better advantage of them
More expensive; better performance
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Considerations When Choosing
Between IDE and SCSI Drives
IDE
SCSI
IDE supports only four internal Supports internal and external
devices
devices; allows additional ones
Separate IRQ required for each
device
Only one IRQ required for
entire chain
Generally backward-compatible Generally backward-compatible
Only one IDE drive on an IDE
channel can be busy at a time
Two or more devices can
operate simultaneously
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More SCSI Considerations

Drives perform better in RAID array

Devices are generally of higher quality and
more expensive

Hard drive with supporting host adapter and
cable costs more than an IDE hard drive
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More SCSI Considerations
(continued)

Subsystem provides faster data transfer

Generally provides better performance


Often used on high-demand servers
A good SCSI host adapter allows connection
of other SCSI devices to it
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Basic Steps for Installing SCSI
Devices
1. Set jumpers or switches on host adapter;
install it on motherboard; install host adapter
drivers
2. Assign SCSI ID with jumpers or switches
3. Attach cabling to host adapter and each device
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Basic Steps for Installing SCSI
Devices (continued)
4. Verify termination at both ends of SCSI chain
5. Power up one device at a time
6. Install drivers and software needed to interface
between SCSI subsystem and OS
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Installing a Host Adapter Card

Install card in expansion slot

Change/verify default settings (setup program)

Verify settings (Advanced Configuration
Options)
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Installing a Host Adapter Card
(continued)

Windows supports host adapter

Loads device drivers automatically and installs
host adapter

Verify correct installation of host adapter
(Device Manager)

Install external SCSI device
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Installing an External SCSI
Device

Install software to run device (includes driver)

Plug SCSI cable into host adapter port

Plug other end of cable into device

Set SCSI ID and install terminator on device


Connect device’s power cord to wall outlet;
turn on device
Restart PC and test device
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Setting Device IDs During
Installation

Assigned automatically with SCAM-compliant
SCSI subsystem

Set manually without SCAM compliance; each
ID must be unique

For narrow SCSI, use IDs 0-7

For wide SCSI, use IDs 0-15

Host adapter usually has ID 7
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Setting Device IDs During
Installation (continued)

For external device:


Push-button or rotary selector
For internal device:

Set of jumpers on the device
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Setting IDs for External Devices
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Setting IDs for Internal Devices
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Installing a SCSI Hard Drive

Host adapter and cables must be compatible
with SCSI drive

Configure SCSI host adapter and SCSI hard
drive to communicate with each other:
1. Set SCSI IDs
2. Disable/enable disk drive and hard drive controllers
3. Check terminating resistors
4. Run CMOS setup for a SCSI system
5. Load SCSI device drivers
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SCSI Hard Drives Connectors
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General Tips for
Troubleshooting SCSI Devices

Keep notes and read documentation

Add one SCSI device at a time

Use good quality components

Limit cable length
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Troubleshooting SCSI
Installation Problems

Turn on external devices first, then computer

Check all connections

Check termination (common cause of
problems)

Verify most updated BIOS

Install PCI host adapter in PCI bus that
supports bus mastering
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Troubleshooting SCSI Boot
Problems

Confirm BIOS setup drive configuration is set
to “No Drives Installed”

Verify that SCSI drive is partitioned, has a
primary partition, and boot partition is set as
active

Back up SCSI hard drive and do low-level
format on it
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Summary

How SCSI technology works to provide better
performance and greater expansion capabilities
for many internal and external devices

Advantages and disadvantages of SCSI

Installation and troubleshooting guidelines
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