Adaptec CDP-00277-01-A - How Is SAS Different from Parallel SCSI

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
mode
Maximum 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 Connections on page 62) 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-congured by SAS devicesUser intervention required to set SCSI IDs
Requires no bus terminationRequires bus termination
SAS connectors (see Cables on page 23)Standard SCSI connectors
63Proprietary and Condential to PMC-Sierra, Inc.
Document No.: CDP-00277-01-A Rev. A, Issue:
Serial Attached SCSI RAID Controllers Installation and User's Guide