Serial attached SCSI is a method

used to access computer

peripheral devices. It employs the

digital data transfer over the thin

cable. In business enterprise it is

used to acess the mass storage

devices.

Introduction to the SAS

SCSI is the acronym of small

computer system interface. It

defines a logical standard to

which disk devices must adhere.

This standard called common

command set. It is a type of

parallel bus.

What is SCSI

This interface is a set of standerd

for physically connecting and

transfer of data between

peripheral devices.

Introduction to SCSI

1) Initiator.

2) Target.

3) Service delivary subsystem.

4) Expanders.

Basic component of

SAS

It is a device that originate device

service and task management

system. It processing by the

target device. It is provided as on

board component in the

motherboard or as a host bus

adapter.

Initiator

A device containing logical unit

and target ports that receives

device service and task

management request. It could be

a hard disk or a disk array

system.

Target

It is a part of a I/O system that

transmit information between

initiator and target. Typecally

cable connecting beteen these

devices.

Service delivery

subsystem

It is a part of device delivary

system and faciliate connection

between SAS devices.

Expanders

There are many different types of

SAS. These are SFF 8482, SFF

8484, SG_XPCIE8SAS_E_Z etc.

Example of SAS

SAS uses point to point

architecture that data between

two different SCSI devices. It uses

differential signaling for achieving

reliable and high speed

communication. It inherits it’s

command set from parallel SCSI

and uses full duplex

communication in the fibre

channel. It uses SAS 2 protocol

it’s link rate is 6.2 Gb/s.

SAS Protocol

SAS support active cables, those

are thin cables with active

circuitry to reduce cable weight

and management. Active circuitry

have build in driver, repeaters and

equalizing filter. It removes the ISI

(inter symbol interference), it is a

type of distorted signal. Driver

and repeater increased the signal

to noise ratio by up raising the

near end cross talk (NEXT).

Cables of SAS

Topology is a arrangement of

links, nodes or computers. It may

also be called as the structure of

network. LAN is a type of physical

topology. SAS has different types

of topology. Mainly internal and

external. There are lots of other

also.

In this topology RAID system use

SAS or SATA drivers. Each drive

has point to point connection with

the controllers. Maximum eight

drives are supported by

controllers. A full height HP smart

expender card support eight

internal drives.

Internal Topology

In this type of topology the

controller connecting to the

external storage enclosure. Each

controller port incorporate four

lanes and total maximum

throughput 2400 MB/s. The

storage enclosure contains

internal 36 port expanders.

External Topology

SAS using this topology it is an

alternative to the fibre channel

local loop topology. It gives you a

high availability with no point of

failure.

Multi Node Cluster

T10 technological committee

SCSI defines as interconnection

of two or more SCSI devices.

When any part of data pathway

domains fails then data transfer

has stop because there is no

redundant pathway. But in this

architecture creates dual path

dual domain and redundant

pathway for storage.

Dual Path Dual Domain

Architecture

Zoning breaks topology into

different logical group for better

traffic management. It gives

unique ID in each expander PHY

to provide secure method for

managing SAS devices. All device

within zone group can interact

with each other.

Zoning

SAS uses mini SAS 4X external

cable plug to connect to the end

devices with enclosure universal

port. Connector can attached with

the out of an enclosure or in port

of an enclosure. Connector have

icon to identify the type of

enclosure. It has a reverse key

allow them to accept SAS 2 cable

longer than 6 m.

SAS cable

SAS technology with different

signaling and active cable

continue to evolve and improve. If

you looking for high level

redundancy then dual domain

and dual path configuration helps

you. It increased the data

availability into the storage

network. Data availability is

essential for uninterrupted of

business operation.

Conclusion

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