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Lesson 10-SCSI

Lesson 10-SCSI. Overview. SCSI chains and host adapters. Different flavors of SCSI. Installing SCSI devices. Basic SCSI troubleshooting. SCSI Chains and Host Adapters. SCSI is a private expansion bus of devices, such as hard drive and CD-ROM, used by the PC.

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Lesson 10-SCSI

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  1. Lesson 10-SCSI

  2. Overview • SCSI chains and host adapters. • Different flavors of SCSI. • Installing SCSI devices. • Basic SCSI troubleshooting.

  3. SCSI Chains and Host Adapters • SCSI is a private expansion bus of devices, such as hard drive and CD-ROM, used by the PC. • When SCSI devices are daisy-chained in a series, they form a sequence called a SCSI chain.

  4. SCSI Chains and Host Adapters • Introduction to SCSI chains and host adapters. • SCSI IDs. • Termination.

  5. Introduction to SCSI Chains and Host Adapters • SCSI devices are daisy-chained in a series called a SCSI chain that connects to the PC through a device called a host adapter. • External SCSI devices stand alone outside the system unit and are hooked to the external connector of the host adapter.

  6. Introduction to SCSI Chains and Host Adapters • Internal devices all connect through a 68-pin ribbon cable, so they do not need a second connector. • A SCSI cable may have from 2 to 15 connectors for internal devices and the host adaptor itself.

  7. SCSI IDs • The SCSI ID number allows the host adaptor to differentiate between devices when they are all connected to the same cable. • To differentiate devices, SCSI uses a unique identifier called SCSI ID. • SCSI device uses jumpers, dip switches, or tiny dials to set the SCSI ID. • The SCSI ID number can range from 0 to 15.

  8. Termination • SCSI chains are vulnerable to reflection. • Reflection is what happens when a signal sent down a long wire reflects back along the wire, causing interference. • Terminators are devices used on the ends of SCSI chain to prevent reflection of electronic signals on the chain.

  9. Different Flavors of SCSI • SCSI-1. • SCSI-2. • SCSI-3. • Mixing flavors.

  10. SCSI-1 • SCSI-1 standard, approved in 1986, defined standard connections, cable lengths, and signaling characteristics. • SCSI-1 is distinguished by its use of internal 50-pin connector cables.

  11. SCSI-1 • SCSI-1 only used 8 of the 50 wires (1 byte) to transfer data. For this reason, this flavor became known as Narrow SCSI. • SCSI-1 allowed a maximum of 8 devices on a single cable, running at a clock rate of 5 MHz.

  12. SCSI-2 • The SCSI-2 standard was officially adopted in 1994. • SCSI-2 introduced Wide SCSI, which meant that data would be moved in two-byte chunks as opposed to one byte.

  13. SCSI-2 • Fast-20 (also called Ultra) and Fast-40 (also called Ultra2) came in narrow and long varieties using a new type of termination called active termination. • SCSI-2 required a new type of termination, called active termination.

  14. SCSI-3 • SCSI-3 lumps all previous cabling and connection options with new ones under a technology called Parallel SCSI. • SCSI-3 speeds up data throughput by using faster signaling and more advanced terminators.

  15. SCSI-3 • Fast-80 and Fast-160 send two signals with each clock cycle. Both are available only in Wide versions. • Moving data at very high speeds requires the use of more powerful terminators called Low Voltage Differential (LVD) terminators.

  16. Mixing Flavors • Faster devices connected to slower host adaptors will run, but at the slower speed. • Cables with one type of connector at one end and another type at the other are common. • Narrow and Wide SCSI can sometimes be mixed, but with less chance of success.

  17. Installing SCSI Devices • Buying a host adapter. • Termination and SCSI IDs. • Installation and host adapter settings. • Drivers. • EIDE and SCSI.

  18. Buying a Host Adapter The following must be considered while buying a host adapter: • The host adapter must use the right connector. • The host adapter should run at the speed of the device. • The host adapter must have onboard BIOS that allows handy tests to be performed without booting to the operating system. • When buying cables for internal devices, consider buying a cable with extra connections for attaching other devices at a later time.

  19. Termination and SCSI IDs • Almost all SCSI devices, including host adapters, have built-in termination. • Checking and recording the SCSI IDs during installation allows for easier setup of new devices later. • Host adaptors are always preset to 7 and no device will ever be preset to 7.

  20. Installation and Host Adapter Settings • Users can change the SCSI ID of the host adaptor and set its termination. • Show Devices, also referred to as Scan Bus, scans the SCSI chain, and displays the names of all properly configured devices. • Disk Utilities configures only the SCSI hard drives. • Device setup performs special configurations for each device on the SCSI chain.

  21. Installation and Host Adapter Settings Disk Utilities provides two choices: • Verify Disk option ensures that the disk is ready to receive data. • The Format Disk command performs a low-level formatting to clean up SCSI drives that may be acting badly.

  22. Drivers • If an SCSI device is installed physically, it shows up in Device Manager. • When a SCSI chain is installed, at least two drives are needed - one for the host adapter and the other for the SCSI device.

  23. EIDE and SCSI • A standard PC with onboard EIDE supports SCSI hard drives. • Systems will first try to boot to the EIDE drives. If it is unable to find the EIDE drive, then it goes to the SCSI drives. • Some systems have a single EIDE drive that stores the operating systems, while the SCSI host adapter has three or more drives that stores critical data.

  24. Basic SCSI Troubleshooting • The SCSI CD-ROM drive automatically appears in My Computer, while the SCSI tape backup device appears in Windows backup program. • If multiple copies of the same device appear, then two devices have been assigned the same SCSI ID.

  25. Basic SCSI Troubleshooting • If no devices show up, then a mistake has been made in the termination. • If only some devices show up, then either the missing devices does not have power or the chain between the host adapter and the missing device has been terminated.

  26. Summary • SCSI devices are daisy-chained together in a series called a SCSI chain. • SCSI chains connect to the PC through the host adapter and the chains must be terminated. • Each device must have a unique SCSI ID and may be internal or external.

  27. Summary • There are three SCSI standards - SCSI-1, SCSI-2, and SCSI-3. • Host adapters must have proper connections and speed to connect to the SCSI devices. • The SCSI devices may show multiple copies, no devices, or some devices may be missing.

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