Data transmission speeds reach about 320 MB per second between the system and the device
Allows to attach 15 devices to a single SCSI port
SCSI controller boosts the signals and enables the devices to be connected at a distance of about 25 meters from the system
Reduces the processing load on the microprocessor, as they have a micro-controller built into the device
Communication problems between the system and SCSI device are reduced as the ends of the SCSI have terminators
SCSI – 1 - Uses an 8-bit parallel bus to transfer data at a maximum speed of 5 MB per second. Can connect up to 8 devices with a cable length of 6 meters and uses passive terminators
SCSI – 2 - Uses a 16-bit bus to transfer data at a maximum speed of 20 MB per second. Can connect up to 16 devices and cable length of 3 meters. Uses 50 pin connector, command queuing feature and active terminator
SCSI – 3 - Uses a 16-bit bus to transfer data at a maximum speed of 40 MB per second. Can connect up to 32 devices and cable length is 3 meter. Uses active terminators
Narrow SCSI – Transmits data over an 8-bit bus. Uses 50 pin connector cable known as A cable
Wide SCSI – Transmits data over a 16-bit bus. Uses 68 pin connector cable known as P cable
Fast SCSI – Transfers the data at the speed of 10 MB per second using the narrow SCSI
Wide Ultra – Transmits data at a speed of 20 MB per second for the narrow SCSI
SCSI Drive speeds – Available at speeds of 10,000 rpm to 15,000 rpm
Universal hard drive – Easy to upgrade the server hard drives and supports S.M.A.R.T feature
Serial Attached SCSI (SAS) – Allows much higher speed data transfer than previously available and is backward comaptible with SATA. Uses SCSI commands for interacting with SAS devices
Single-Ended (SE) – Transmits a positive voltage through a signal line to the receiver. Maximum cable length is 6 meter
Low-Voltage Differential (LVD) – Signals are transmitted using the difference in the voltage between the two wires. SCSI device adapter has a small transceiver built into it which boosts signal. Easily integrates up to 16 devices on SCSI bus using 12 meter of cable. Uses 3.3 voltage to represent logical 1 or 0
High-Voltage Differential (HVD) – Reduces problems of bouncing signals, signal interference problems, noise and crosstalk. Enables cable length up to 25 meters. It is very costly
Low-Voltage Differential/ Single - Ended Multi-mode (LVD/SE) – Compatible with LVD and SE signaling. However if there is a device that uses SE signaling on SCSI bus, then this will be set to use SE signaling
Jumper Block/ DIP Switch Settings – SCSI identification is set using software available with SCSI device, using the jumpers or switches on the SCSI device
Resolving Id Conflicts – SCSI identification specifies the priority in which the device has access to the bus. Host SCSI controller on the system is generally given the highest SCSI priority 7 to ensure that it gets first access to system resources. SCSI hard drives are factory set to have ID 0
Internal Connectors – Located on SCSI devices such as hard disks and CD drives that are installed inside the system case
External Connectors – Located on the SCSI adapters and the SCSI devices such as printers, scanners and external tape drives
Type :
Internal SCSI Cable – Flat ribbon cable
External SCSI Cables – Thick round cable
Termination Requirements :
Redundant Array of Inexpensive Disks (RAID) - RAID is a collection of hard disks that appear to the system as a single disk
Installing the Host Adapter – Given the highest priority over SCSI bus so that it can serve other devices properly
Installing the Internal SCSI Device – Connects to the host adapter bus using the SCSI cable
Installing the External SCSI Devices – Connects external devices such as SCSI scanners and printers to the system
Problem with the SCSI Daisy-Chain –
In a daisy chain any problem with any one device may cause all the devices to malfunction
Check that the power supply is switched on for all the devices
Check that the cables in the daisy-chain are properly connected and not loose
Check that both ends of the SCSI daisy-chain are terminated
Check that the SCSI ID is not repeated for two or more devices
Disconnect all the devices and reconnect them one by one
Reinstall the device drivers
The Connected Device is not Functioning Properly -
Check if the devices are connected properly
Ensure that the terminators are secured properly at the ends of the SCSI daisy-chain
Change the SCSI ID of the device
Reinstall the device driver
Small Computer Systems Interface (SCSI) enables you to attach peripherals to the system
SCSI consists of controller, cables and the device
Advantages of SCSI :
SCSI standards specify the features of SCSI devices
SCSI bus signaling specifies the method used by the SCSI devices to communicate with each other
Different SCSI signaling methods :
The SCSI ID specifies the priority of the SCSI device on the SCSI bus
SCSI connectors enable you to affix the SCSI cable to the SCSI adapter or the SCSI device
The SCSI terminator is used to terminate the SCSI daisy-chain
Active terminators have a resistor and also a voltage regulator
RAID is a collection of hard disks that appear to the system as a single disk
Hot swap drives enable you to connect and disconnect drives to the system without shutting down or restarting the system
Installing SCSI host adapter, internal and external SCSI drives
