A.11 How is SAS Different from Parallel SCSI?
In summary, although SAS and parallel SCSI both use the SCSI command set, how they move data from one
place to another is very different. To support point-to-point serial data transport, SAS introduces new types
of connectors, cables, connection options, and terminology.
Generally speaking, SAS is faster and more exible than parallel SCSI, and provides more options for building
your storage space. SAS lets you mix SAS and SATA disk drives together, and lets you connect many, many
more devices.
This table describes many of the main differences between the two interfaces.
Serial Attached SCSIParallel SCSI
Serial interfaceParallel interface
Maximum speed 300 MB/sec per phy when in half-duplex modeMaximum speed 320 MB/sec shared by all devices on the
bus
Supports SATA and SAS disk drives simultaneouslySupports SCSI devices only
More than 100 disk drives per SAS card, using an expander (see
SAS Expander ConnectionsSAS expander connectionsexpander
connections) or 50 SATAII disk drives.
Up to 16 devices per SCSI channel
Supports single- and dual-port devicesSupports single-port devices only
Uses unique SAS addresses to differentiate between devicesUses SCSI IDs to differentiate between devices connected
to the same adapter
SAS addresses self-congured by SAS devicesUser intervention required to set SCSI IDs
Requires no bus terminationRequires bus termination
SAS connectors (see Cablescontrollers SAS cablesSAS cables)Standard SCSI connectors
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Microsemi Proprietary and Condential. Installation and User's Guide Revision 5
Introduction to SAS
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