Chapter 8
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Presentation Transcript
Chapter 8 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 • Some 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 • Faster, more expensive, more difficult to install than similar IDE devices
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
The SCSI Subsystem • Every SCSI bus subsystem requires a SCSI controller and unique SCSI IDs assigned to each device, including the host adapter
Issues to Consider when Selecting a Host Adapter • BIOS • Expansion slot • Bus mastering
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 • Bus width • Signaling methods used on SCSI cables • Connectors used with SCSI cables • Termination • SCSI-1, SCSI-2, and SCSI-3
Bus Width • Narrow SCSI (8 bits) • Wide SCSI (16 bits)
Signaling Methods Usedon 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)
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
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 SCSI-1, SCSI-2, and SCSI-3
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
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
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
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
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
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
Troubleshooting SCSI Devices • General tips • Installation problems • Booting problems
General Troubleshooting Tips • Keep notes and read documentation • Add one SCSI device at a time • Use good quality components • Limit cable length
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
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 • Advantages and disadvantages of SCSI
