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  1. 1. A+ Guide to Managing and Maintaining Your PC Fifth Edition Chapter 22 All About SCSI
  2. 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  Troubleshooting tips for SCSI 2
  3. 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 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 3
  4. 4. 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 4
  5. 5. SCSI Host Adapter 5
  6. 6. IDE versus SCSI Bus Communication 6
  7. 7. Host Adapters  Manage all devices on SCSI bus  Support internal and external SCSI devices  Form a single daisy chain with devices 7
  8. 8. Considerations When Selecting a Host Adapter  BIOS  Expansion slot  Bus mastering  SCAM-compliant 8
  9. 9. 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 9
  10. 10. Expansion Slot Considerations  Host adapter must fit expansion slot (eg, 16-bit ISA, PCI) 10
  11. 11. 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 11
  12. 12. 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 12
  13. 13. 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) 13
  14. 14. Variations in SCSI  Bus width  Signaling methods used on SCSI cables  Connectors used with SCSI cables  Termination  SCSI-1, SCSI-2, and SCSI-3 14
  15. 15. 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) 15
  16. 16. 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 16
  17. 17. Signaling Methods Used on SCSI Cables (continued) 17
  18. 18. SCSI Cables 18
  19. 19. Signaling Symbols 19
  20. 20. 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 20
  21. 21. SCSI Connectors 21
  22. 22. Multiple Connectors on the SCSI Bus 22
  23. 23. Termination  Prevents echo effect from electrical noise and reflected data at end of SCSI daisy chain  Required at each end of a SCSI chain 23
  24. 24. 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 24
  25. 25. External SCSI Terminator 25
  26. 26. 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 26
  27. 27. 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 27
  28. 28. 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 28
  29. 29. SCIS Standards 29
  30. 30. SCIS Standards (continued) 30
  31. 31. SCIS Standard Cable Specs 31
  32. 32. 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 32
  33. 33. 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 33
  34. 34. 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 34
  35. 35. 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 35
  36. 36. Basic Steps for Installing SCSI Devices 1. 2. 3. 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 36
  37. 37. 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 37
  38. 38. Installing a Host Adapter Card  Install card in expansion slot  Change/verify default settings (setup program)  Verify settings (Advanced Configuration Options) 38
  39. 39. 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 39
  40. 40. 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 40
  41. 41. 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 41
  42. 42. Setting Device IDs During Installation (continued)  For external device:   Push-button or rotary selector For internal device:  Set of jumpers on the device 42
  43. 43. Setting IDs for External Devices 43
  44. 44. Setting IDs for Internal Devices 44
  45. 45. 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 45
  46. 46. SCSI Hard Drives Connectors 46
  47. 47. 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 47
  48. 48. 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 48
  49. 49. 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 49
  50. 50. 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 50