Adaptec 6805Q 2270700-R User Manual
Product codes
2270700-R
Appendix A: Introduction to 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.
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.
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
devices on the bus
Maximum speed 300 MB/sec per phy when in half-
duplex mode
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
expander (see
) 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
devices connected to the same adapter
Uses unique SAS addresses to differentiate
between devices
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