Appendix A: Introduction to Serial Attached SCSI (SAS)
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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.
The table below 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
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
)
