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The following figure illustrates (in very basic terms) a SAS domain and shows how SAS cards,
SAS and SATA disk drives, and expander devices can fit together in a large data storage
topology.
SAS
Disk Drives
SAS
SAS Card
SAS
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 following table describes many of the main differences between the two interfaces.
Parallel SCSI
Parallel interface
Maximum speed 320 MB/sec
shared by all devices on the bus
Supports SCSI devices only
Up to 16 devices per SCSI
channel
Supports single-port devices only
Uses SCSI IDs to differentiate
between devices connected to
the same adapter
User intervention required to set
SCSI IDs
Requires bus termination
Standard SCSI connectors
SAS Domain
SAS Domain
SATA
Disk Drives
SATA
Disk Drives
SATA
SAS
Fanout Expander
SAS Card
SATA
SAS
SATA
Disk Drives
Disk Drives
Serial Attached SCSI
Serial interface
Maximum speed 600 MB/sec per phy
when in full-duplex mode
Supports SATA and SAS disk drives
simultaneously
More than 128 disk drives per SAS
card, using an expander (see
Supports single- and dual-port
devices
Uses unique SAS addresses to
differentiate between devices
SAS addresses self-configured by
SAS devices
Requires no bus termination
SAS connectors (see
Appendix A: Introduction to SAS
SATA
Disk Drives
SATA
SAS Card
SATA
Disk Drives
SAS
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