All About SCSI

1
Chapter 8

• All About SCSI

2
You Will Learn

• About basics of SCSI technology and components
• How SCSI hard drives compare to IDE drives
• How to install a SCSI device
• Some troubleshooting tips for SCSI

3
SCSI Basics

• SCSI Small Computer System Interface
• Standard for communication between subsystem of
  peripheral devices and system bus
• Bus can contain/be used by up to 7 or 15 devices
• Bus controller can be either
• An expansion card (host adapter)
• Embedded on motherboard
• Faster, more expensive, more difficult to install
  than similar IDE devices

4
The SCSI Subsystem

• Host adapter
• Card inserted onto expansion slot on mother board
• Manages all devices on SCSI bus
• Supports internal and external SCSI devices
• Forms a single daisy chain with devices
• Device drivers
• Enable OS to communicate with a host adapter

5
The SCSI Subsystem
6
IDE vs. SCSI Bus Communication
7
Issues to Consider when Selecting a Host Adapter

• BIOS
• Expansion slot
• Bus mastering
• SCAM-compliant

8
Vendors for Host Adapters
9
SCSI Device Drivers

• ASPI (Advanced SCSI Programming Interface)
• CAM (Common Access Method)

10
Variations in SCSI

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

11
Bus Width

• Narrow SCSI (8 bits)
• Wide SCSI (16 bits)

12
Signaling Methods Usedon SCSI Cables

• Single-ended (SE)
• Differential

13
Signaling Methods on SCSI Cables
14
SCSI Cables
15
Signaling Methods on SCSI Cables
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Connectors for SCSI Cables
17
Connectors for SCSI Cables
18
Termination

• Prevents echo effect from electrical noise and
  reflected data at end of SCSI daisy chain
• Types used with single-ended SCSI cables
• Passive terminators
• Active terminators
• Forced perfect terminators (FPTs)
• Types used with differential cables
• HVD terminators
• LVD terminators

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Termination
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SCSI-1, SCSI-2, and SCSI-3

• SCSI-1 Regular SCSI
• 8-bit data bus
• 7 possible devices
• SCSI-2 Fast SCSI
• Common command set
• 16-bit data bus
• 15 possible devices
• Mandatory parity checking

• SCSI-3 Ultra SCSI
• Supports both parallel and serial data
  transmission
• Supports FireWire connections
• Data transfer of 320 MB/sec

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Summary of SCSI Standards
22
SCSI Standard Cable Specs
23
Comparing IDE and SCSI

• SCSI is more expensive
• IDE gives better performance

24
SCSI Installation

• Set jumpers or switches on host adapter and
  install it on motherboard
• Assign the SCSI ID with jumpers or switches
• Attach cabling to host adapter and each device
• Verify termination at both ends of daisy chain
• Power up one device at a time
• Install drivers and software

25
Setting Device IDs During Installation
26
Setting Device IDs During Installation
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Installing a SCSI Hard Drive

• 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

28
Troubleshooting SCSI Devices

• General tips
• Installation problems
• Booting problems

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General Troubleshooting Tips

• Keep notes and read documentation
• Add one SCSI device at a time
• Use good quality components
• Limit cable length

30
Problems Installing SCSI Devices

• Turn on external devices first, then computer
• Check connections
• Verify correct termination (common cause of
  problems)
• Verify most updated BIOS
• Install PCI host adapter in PCI bus that supports
  bus mastering

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Booting 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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Chapter Summary

• How SCSI technology works
• Advantages and disadvantages of SCSI