1. Chapter 8
All About SCSI

2. 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
Some troubleshooting tips for SCSI

3. 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
Faster, more expensive, more difficult to install than similar IDE devices

4. The SCSI Subsystem Host adapter Device drivers
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
Every SCSI bus subsystem requires a SCSI controller and unique SCSI IDs assigned to each device, including the host adapter

6. The SCSI Subsystem

7. IDE vs. SCSI Bus Communication

8. Issues to Consider when Selecting a Host Adapter
BIOS
Expansion slot
Bus mastering

9. Vendors for SCSI Host Adapters

10. 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)

11. Variations in SCSI Bus width Signaling methods used on SCSI cables
Connectors used with SCSI cables
Termination
SCSI-1, SCSI-2, and SCSI-3

12. Bus Width
Narrow SCSI (8 bits)
Wide SCSI (16 bits)

13. Signaling Methods Used on SCSI Cables
Single-ended (SE)
Send a signal on pair of twisted wires; one carries voltage, the other is a ground
Differential
Send a signal on pair of twisted wires; both carry voltage, and the signal is calculated to be the difference between the two voltages
High Voltage Differential (HVD)
Low Voltage Differential (LVD)

14. Signaling Methods on SCSI Cables

15. SCSI Cables

16. Signaling Methods on SCSI Cables

17. Connectors for SCSI Cables

18. Connectors for SCSI Cables

19. Termination
Prevents echo effect from electrical noise and reflected data at end of SCSI daisy chain
Single-ended SCSI cables use:
Passive terminators
Active terminators
Forced perfect terminators (FPTs)
Differential cables use either HVD or LVD terminators

20. Termination

21. SCSI-1, SCSI-2, and SCSI-3 SCSI-1 = Regular SCSI SCSI-2 = Fast 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

24. 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…

25. 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…

26. 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

27. SCSI Installation
Set jumpers or switches on host adapter and install it on motherboard
Assign 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

28. Installing a Host Adapter Card with Windows 9x/2000/XP
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

29. Installing a Host Adapter Card with Windows 9x/2000/XP

30. Installing a Host Adapter Card with Windows 9x/2000/XP

31. Setting Device IDs During Installation
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 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

32. Setting Device IDs During Installation
To set IDs for external devices, use either push-button selector or rotary selector
To set IDs for internal device, use set of jumpers on the device

33. Setting External Device IDs

34. Setting Internal Device IDs

35. Installing a SCSI Hard Drive
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:
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

36. Troubleshooting SCSI Devices
General tips
Installation problems
Booting problems

37. General Troubleshooting Tips
Keep notes and read documentation
Add one SCSI device at a time
Use good quality components
Limit cable length

38. 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

39. 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

40. Chapter Summary
How SCSI technology works to provide better performance and greater expansion capabilities for many internal and external devices
Advantages and disadvantages of SCSI