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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. SCSI Basics. Standard for communication between subsystem of peripheral devices and system bus

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chapter 22

Chapter 22

All About SCSI

you will learn
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

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

scsi basics
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

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

the scsi subsystem
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

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

scsi host adapter
SCSI Host Adapter

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

ide versus scsi bus communication
IDE versus SCSI Bus Communication

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

host adapters
Host Adapters
  • Manage all devices on SCSI bus
  • Support internal and external SCSI devices
  • Form a single daisy chain with devices

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

considerations when selecting a host adapter
Considerations When Selecting a Host Adapter
  • BIOS
  • Expansion slot
  • Bus mastering
  • SCAM-compliant

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

bios considerations
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

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

expansion slot considerations
Expansion Slot Considerations
  • Host adapter must fit expansion slot(eg, 16-bit ISA, PCI)

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

bus mastering
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

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

scam compliant
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

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

scsi device drivers
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)

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

variations in scsi
Variations in SCSI
  • Bus width
  • Signaling methods used on SCSI cables
  • Connectors used with SCSI cables
  • Termination
  • SCSI-1, SCSI-2, and SCSI-3

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

bus width
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)

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

signaling methods used on scsi cables
Signaling Methods Used on SCSI Cables

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

signaling methods used on scsi cables continued
Signaling Methods Used on SCSI Cables (continued)

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

scsi cables
SCSI Cables

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

signaling symbols
Signaling Symbols

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

connectors used with scsi cables
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

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

scsi connectors
SCSI Connectors

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

multiple connectors on the scsi bus
Multiple Connectors on the SCSI Bus

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

termination
Termination
  • Prevents echo effect from electrical noise and reflected data at end of SCSI daisy chain
  • Required at each end of a SCSI chain

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

ways to terminate the end of a scsi chain
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

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

external scsi terminator
External SCSI Terminator

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

terminators
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

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

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

Major Versions of SCSI

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

major versions of scsi continued
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

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

scis standards
SCIS Standards

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

scis standards continued
SCIS Standards (continued)

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

scis standard cable specs
SCIS Standard Cable Specs

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

comparing ide and scsi
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

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

considerations when choosing between ide and scsi drives
Considerations When Choosing Between IDE and SCSI Drives

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

more scsi considerations
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

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

more scsi considerations continued
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

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

basic steps for installing scsi devices
Basic Steps for Installing SCSI Devices
  • Set jumpers or switches on host adapter; install it on motherboard; install host adapter drivers
  • Assign SCSI ID with jumpers or switches
  • Attach cabling to host adapter and each device

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

basic steps for installing scsi devices continued
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

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

installing a host adapter card
Installing a Host Adapter Card
  • Install card in expansion slot
  • Change/verify default settings (setup program)
  • Verify settings (Advanced Configuration Options)

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

installing a host adapter card continued
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

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

installing an external scsi device
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

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

setting device ids during installation
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

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

setting device ids during installation continued
Setting Device IDs During Installation (continued)
  • For external device:
    • Push-button or rotary selector
  • For internal device:
    • Set of jumpers on the device

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

setting ids for external devices
Setting IDs for External Devices

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

setting ids for internal devices
Setting IDs for Internal Devices

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

installing a scsi hard drive
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:
    • Set SCSI IDs
    • Disable/enable disk drive and hard drive controllers
    • Check terminating resistors
    • Run CMOS setup for a SCSI system
    • Load SCSI device drivers

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

scsi hard drives connectors
SCSI Hard Drives Connectors

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

general tips for troubleshooting scsi devices
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

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

troubleshooting scsi installation problems
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

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

troubleshooting scsi boot problems
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

A+ Guide to Managing and Maintaining Your PC, Fifth Edition

summary
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

A+ Guide to Managing and Maintaining Your PC, Fifth Edition