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 flexible 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.

Parallel SCSI

Serial Attached SCSI

Parallel interface

Serial interface

Maximum speed 320 MB/sec shared by all devices on the bus

Maximum speed 300 MB/sec per phy when in half-duplex mode

Supports SCSI devices only

Supports SATA and SAS disk drives simultaneously

Up to 16 devices per SCSI channel

More than 100 disk drives per SAS card, using an expander (see SAS Expander Connections) or 50 SATAII disk drives.

Supports single-port devices only

Supports single- and dual-port devices

Uses SCSI IDs to differentiate between devices connected to the same adapter

Uses unique SAS addresses to differentiate between devices

User intervention required to set SCSI IDs

SAS addresses self-configured by SAS devices

Requires bus termination

Requires no bus termination

Standard SCSI connectors

SAS connectors (see Cables)

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