Introduction to the SAS

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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
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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
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This interface is a set of standerd for
physically connecting and transfer of data
between peripheral devices.
Introduction to SCSI
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1) Initiator.2) Target3) Service delivary
subsystem4) Expanders
Basic component of SAS
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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
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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
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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
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It is a part of device delivary system and
faciliate connection between SAS devices.
Expanders
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There are many different types of SAS. These are
SFF 8482, SFF 8484, SG_XPCIE8SAS_E_Z etc.
Example of SAS
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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 its
command set from parallel SCSI and uses full
duplex communication in the fibre channel. It
uses SAS 2 protocol its link rate is 6.2 Gb/s.

SAS Protocol
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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
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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.
SAS Topologies
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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
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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
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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
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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
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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
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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
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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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THANK YOU