Adaptec 1045 User Guide - Page 55

How is SAS Different from Parallel SCSI?, SAS Domain

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Chapter A: Introduction to SAS l 55 You can use only one fanout expander in any single SAS domain (a topology of SAS-and possibly SATA-end devices and expander devices). A single SAS domain can therefore comprise up to 16,384 SAS ports (and therefore up to 16,384 SAS addresses). The following figure illustrates (in very basic terms) a SAS domain and shows how SAS controllers, SAS and SATA disk drives, and expander devices can fit together in a large data storage topology. SAS Domain Disk Drives SAS SAS SATA Disk Drives SATA Disk Drives SATA SAS Edge Expander SATA Disk Drives SATA Edge Expander Edge Expander SAS Card SAS SATA Disk Drives Edge Expander Fanout Expander SAS Card SAS SATA Disk Drives Edge Expander SAS Card SATA Disk Drives SAS How is SAS Different from Parallel SCSI? In summary, although SAS and parallel SCSI 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 Serial Attached SCSI Serial interface Maximum speed 600 MB/sec per phy when in full-duplex mode Supports SAS and SATA disk drives simultaneously More than 128 disk drives per SAS controller, using an expander (see page 54) Supports single- and dual-port devices Uses unique SAS addresses to differentiate between devices SAS addresses self-configured by SAS devices

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Chapter A: Introduction to SAS
l 55
You can use only one fanout expander in any single SAS domain (a topology of SAS—and
possibly SATA—end devices and expander devices). A single SAS domain can therefore
comprise up to 16,384 SAS ports (and therefore up to 16,384 SAS addresses).
The following figure illustrates (in very basic terms) a SAS domain and shows how SAS
controllers, SAS and SATA disk drives, and expander devices can fit together in a large data
storage topology.
How is SAS Different from Parallel SCSI?
In summary, although SAS and parallel SCSI 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.
SAS Card
SAS Card
Disk Drives
Disk Drives
Disk Drives
Disk Drives
Disk Drives
Disk Drives
Fanout Expander
Disk Drives
Edge
Expander
Edge
Expander
SATA
SATA
SATA
SATA
SAS
SAS
SAS
SATA
Edge
Expander
SATA
SATA
SAS
SAS
Edge
Expander
Edge
Expander
SAS Card
SAS Domain
SAS Domain
SATA
SAS
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 SAS and SATA disk drives
simultaneously
Up to 16 devices per SCSI channel
More than 128 disk drives per SAS
controller, using an expander (see
page
54
)
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