Transcript Presentation

Chapter 22
All About SCSI
You Will Learn…
 About basics of SCSI (Small Computer System
Interface) 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
 Bus can contain/be used by up to 7 or 15
devices, depending on SCSI standard
 Bus controller can be either:
• An expansion card (host adapter)
• Embedded on motherboard
The SCSI Subsystem
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Host adapter
• Gateway from the SCSI bus to the system bus
• 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
Two devices on SCSI bus can pass data between them
without going through CPU; convenient for back up
The SCSI Subsystem
IDE vs. SCSI Bus Communication
The SCSI Subsystem
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SCSI drive has its controller mounted inside the drive
housing and can have a variable number of sectors per
track
Each end of the SCSI chain has a terminating resistor
Each device on the bus is assigned a SCSI ID
Two important components
• Host adapters
• Device drivers
Host Adapters
 Issues to consider when selecting a host
adapter
• BIOS
• Expansion slot
• Bus mastering
BIOS
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Look for a host adapter that is PnP compatible and
has a configuration utility built into its ROM
Check for software that configures termination and
assigns system resources
Look for a host adapter whose BIOS can configure
SCSI devices using the bus controlled by the adapter
See how many devices the BIOS supports (up to 15 is
best)
Expansion Slot
 Host adapter must fit the expansion slot you
plan to use
 Choose 32-bit PCI bus for faster data transfer
rate (Pentium motherboard)
Bus Mastering
 Choose a host adapter that supports bus
mastering, if your system bus supports it
SCAM-Compliant
 SCAM = SCSI Configuration AutoMatically
 Method by which SCSI devices and the host
adapter can be PnP compliant
 Two levels (Level 1 and Level2)
Vendors for SCSI Host Adapters
SCSI Device Drivers
 Enable OS to communicate with a host adapter
 Two popular driver types
• ASPI (Advanced SCSI Programming Interface) –
•
more popular of the two
CAM (Common Access Method)
Variations in SCSI
 Standards
 Types of cabling
 Bus widths
Bus Width
 Narrow SCSI (8 bits)
 Wide SCSI (16 bits)
SCSI Cables Signaling Methods
Single-Ended Signaling
 Send a signal on a pair of twisted wires; one
carries voltage, the other is a ground
 Less expensive, but maximum cable length
cannot be as long because data integrity is not
as great
Differential Signaling
 Send a signal on a pair of twisted wires; both
carry voltage, and the signal is calculated to be
the difference between the two voltages
 Better signal accuracy
 Greater reliability and reduction in chance of
data errors
 High Voltage Differential (HVD)
 Low Voltage Differential (LVD)
SCSI Cables
Signaling Symbols
SCSI Cable Connectors
SCSI Cable Connectors
Termination
 Provides an echo effect from electrical noise
and reflected data at the end of the SCSI daisy
chain
Ways to Terminate a SCSI Chain
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Host adapter can have a switch setting that activates
or deactivates a terminating resistor on the card
Device can have either a single SCSI connection or
two connections (external terminator)
Device at end of the chain can be terminated by a
resistor physically mounted on that device
Internal terminator
Controlled by software
Types of Terminators
 Passive terminators
 Active terminators
 Forced perfect terminators (FPTs)
Major Versions of SCSI
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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
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SCSI-3 = Ultra SCSI
• Supports both parallel
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and serial data
transmission
Supports FireWire
connections
Data transfer of 320
MB/sec
SPI (SCSI Parallel
Interface) standards
SCSI Standards
SCSI Cable Specifications
Comparing IDE and SCSI
 IDE supports only four internal devices; SCSI
supports both internal and external and allows
you to add more
 SCSI devices are generally of higher quality
than IDE devices and more expensive
 IDE devices require separate IRQ for each
device; SCSI requires only one for entire chain
continued…
Comparing IDE and SCSI
 Both are generally backward-compatible
 SCSI hard drive with supporting host adapter
and cable costs more than an IDE hard drive
 SCSI subsystem provides faster data transfer
than an IDE drive
 SCSI generally provides better performance
than IDE; often used on high-demand servers
continued…
Comparing IDE and SCSI
 Good host SCSI host adapter allows
connection of other SCSI devices to it
 With SCSI, two or more devices can operate
simultaneously; with IDE, only one IDE drive
on an IDE channel can be busy at a time
Basic Steps for SCSI Installation
1. Set jumpers or switches on host adapter and install
it on motherboard; install host adapter drivers
2. Use jumpers or switches to assign SCSI ID
3. Attach cabling to host adapter and each device
4. Verify termination at both ends of daisy chain
5. Power up one device at a time
6. Install drivers and software
Installing a Host Adapter Card
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Install card in expansion slot
Change/verify default settings using setup program
Verify settings under Advanced Configuration
Options
Windows supports host adapter; it loads device
drivers automatically and installs host adapter
Use Device Manager to verify correct installation of
host adapter
Install external SCSI device
Installing a Host Adapter Card
Installing a Host Adapter Card
Setting Device IDs During Installation
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With SCAM-compliance, SCSI IDs are assigned
automatically
Without SCAM compliance, set device SCSI IDs
manually
• Each ID must be unique; no two devices on same SCSI
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channel can have same ID number
For narrow SCSI, use IDs 0-7
For wide SCSI, use IDs 0-15
Host adapter usually has ID 7
Setting Device IDs During Installation
 To set IDs for external devices, use either
push-button selector or rotary selector
 To set IDs for internal devices, use set of
jumpers on the device
Setting External Device IDs
Setting Internal Device IDs
Installing a SCSI Hard Drive
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Make sure host adapter and cables are compatible
with SCSI drive
Configure SCSI host adapter and SCSI hard drive so
they can communicate with each other as follows:
1.
2.
3.
4.
5.
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
General Troubleshooting Tips
 Keep notes and read documentation
 Add one SCSI device at a time
 Use good quality components
 Limit cable length
Troubleshooting Installation Problems
 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
Troubleshooting 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
Chapter Summary
 How SCSI technology works to provide better
performance and greater expansion capabilities
for many internal and external devices (hard
drives, CD-ROM drives, DVD drives, and
scanners)
 Faster, more expensive, more difficult to install
than similar IDE devices
 Advantages and disadvantages of SCSI