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Appendix A: Introduction to Serial Attached SCSI ● 68
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 600 MB/sec per phy when in full-
duplex mode
Supports SCSI devices only Supports SATA and SAS disk drives simultaneously
Up to 16 devices per SCSI channel
More than 128 disk drives per SAS card, using an
expander (see page 67)
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 page 28)