3.1 - SCSI Device Cables

Question 1

The SCSI standard

Answer 1

• Small Computer Systems Interface
  – Not really “small” any longer
• Originally designed to string many peripherals
  together onto a single cable/controller
  – Up to 16 devices in a SCSI “chain”
• Many different formats
  – Fast SCSI, Ultra SCSI, Ultra Wide SCSI, Ultra2 SCSI,
  – Ultra3 SCSI, Ultra-320 SCSI, Ultra-640 SCSI,
  – iSCSI (SCSI over IP)
• Parallel and serial options

Question 2

SCSI advantages

Answer 2

• Not just for hard drives
  – Scanners, tape drives, CD-ROM drives
• Many devices on a single bus
  – 8 on narrow bus, 16 on wide bus
• Very intelligent interface functionality
  – Much of the difficult configuration work is done
  between the SCSI devices
• Industry longevity
  – Well supported in the enterprise
  – A standard drive for virtual systems

Question 3

SCSI ID and logical unit (LUN)

Answer 3

• Every SCSI device on a single bus is
  assigned a separate ID number
  – SCSI ID 0 (SCSI controller), ID 2 (hard drive), ID 3 (CD-ROM)
• Logical units (LUNs) are defined within each SCSI ID
  – Separate drives in a storage array or virtual machine
• The signal at the “end” of a physical SCSI bus is terminated
  – Can be internal to the device or a
  separate termination device
• Serial attached SCSI (SAS) devices have no
  jumpers, terminators, or settings.

Question 4

Serial attached SCSI

Answer 4

• Move from parallel to serial
  – Increased throughput
  – Similar to the move from PATA to SATA
• Point-to-point connection
  – No more daisy chains
• No termination required
  – The bus has two devices on it
• The control and management of SCSI
  – The speed of a serial connection

Question 5

SCSI example images

Answer 5