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Introduction to the SASSerial attached SCSI is a methodused to access computerperipheral devices. It employs thedigital data transfer over the thincable. In business enterprise it isused to acess the mass storagedevices.

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What is SCSISCSI is the acronym of smallcomputer system interface. Itdefines a logical standard towhich disk devices must adhere.This standard called commoncommand set. It is a type ofparallel bus.

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Introduction to SCSIThis interface is a set of standerdfor physically connecting andtransfer of data betweenperipheral devices.

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Basic component of SAS1) Initiator.2) Target.3) Service delivary subsystem.4) Expanders.

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InitiatorIt is a device that originate deviceservice and task managementsystem. It processing by thetarget device. It is provided as onboard component in themotherboard or as a host busadapter.

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TargetA device containing logical unitand target ports that receivesdevice service and taskmanagement request. It could bea hard disk or a disk arraysystem.

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Service delivery subsystemIt is a part of a I/O system thattransmit information betweeninitiator and target. Typecallycable connecting beteen thesedevices.

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ExpandersIt is a part of device delivarysystem and faciliate connectionbetween SAS devices.

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Example of SASThere are many different types ofSAS. These are SFF 8482, SFF8484, SG_XPCIE8SAS_E_Z etc.

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SAS ProtocolSAS uses point to pointarchitecture that data betweentwo different SCSI devices. It usesdifferential signaling for achievingreliable and high speedcommunication. It inherits it’scommand set from parallel SCSIand uses full duplexcommunication in the fibrechannel. It uses SAS 2 protocolit’s link rate is 6.2 Gb/s.

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Cables of SASSAS support active cables, thoseare thin cables with activecircuitry to reduce cable weightand management. Active circuitryhave build in driver, repeaters andequalizing filter. It removes the ISI(inter symbol interference), it is atype of distorted signal. Driverand repeater increased the signalto noise ratio by up raising thenear end cross talk (NEXT).

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Topology is a arrangement oflinks, nodes or computers. It mayalso be called as the structure ofnetwork. LAN is a type of physicaltopology. SAS has different typesof topology. Mainly internal andexternal. There are lots of otheralso.

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Internal TopologyIn this topology RAID system useSAS or SATA drivers. Each drivehas point to point connection withthe controllers. Maximum eightdrives are supported bycontrollers. A full height HP smartexpender card support eightinternal drives.

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External TopologyIn this type of topology thecontroller connecting to theexternal storage enclosure. Eachcontroller port incorporate fourlanes and total maximumthroughput 2400 MB/s. Thestorage enclosure containsinternal 36 port expanders.

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Multi Node ClusterSAS using this topology it is analternative to the fibre channellocal loop topology. It gives you ahigh availability with no point offailure.

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Dual Path Dual Domain ArchitectureT10 technological committeeSCSI defines as interconnectionof two or more SCSI devices.When any part of data pathwaydomains fails then data transferhas stop because there is noredundant pathway. But in thisarchitecture creates dual pathdual domain and redundantpathway for storage.

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ZoningZoning breaks topology intodifferent logical group for bettertraffic management. It givesunique ID in each expander PHYto provide secure method formanaging SAS devices. All devicewithin zone group can interactwith each other.

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SAS cableSAS uses mini SAS 4X externalcable plug to connect to the enddevices with enclosure universalport. Connector can attached withthe out of an enclosure or in portof an enclosure. Connector haveicon to identify the type ofenclosure. It has a reverse keyallow them to accept SAS 2 cablelonger than 6 m.

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ConclusionSAS technology with differentsignaling and active cablecontinue to evolve and improve. Ifyou looking for high levelredundancy then dual domainand dual path configuration helpsyou. It increased the dataavailability into the storagenetwork. Data availability isessential for uninterrupted ofbusiness operation.

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