3.1 Cables And Adapters: SCSI Drive Cables

Question 1

SCSI Standard

Answer 1

Small Computer Systems Interface
(Not small anymore)

Pronounced- Scusee

Originally designed to string many peripherals together onto a single cable/controller
- up to 16 devices on one chain

Many different formats
- fast SCSI, ultra SCSI, ultra wide SCSI, etc

Parallel (all at once) and serial (executes one at a time) versions

Question 2

SCSI advantages

Answer 2

Allowed for connecting lots of devices, usb connection non existent at time

Many devices on 1 bus

• 8 devices on narrow bus
• 16 on wide bus

Very intelligent interface functionality
- not a lot of configuration, most of difficult configuration is done by the scsi device

Industry longevity

• still in use today
• standard drive for virtual systems

Question 3

SCSI Interface

Answer 3

Many different interfaces

ultra 3 version

• 68 pin
• similar size to PATA interface

Question 4

SCSI ID and logical unit (LUN)

Answer 4

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

Signal at the end of a physical SCSI bus must be terminated
- can be terminated with an internal device or a separate termination device

Newer SCSIs

• don’t use separate ids or luns
• use serial attached SCSI (SAS)
• no termination needed
• one to one connection

Question 5

Serial attached SCSI (SAS)

Answer 5

Move from parallel to serial

• increased throughput
• similar to move from PATA to SATA

Point to point connection
- no more daisy chains

No termination required
- host device on one end storage device on other end

• same control as old version but with high speed connection

Looks like SATA drive

Uses high density internal SAS connector