Adaptec SAS/SATA/SCSI RAID Controllers - Manual (Page 67)

Appendix A: Introduction to Serial Attached SCSI ●
67
SAS Expander Connections
A SAS expander device literally expands the number of end devices that you can connect
together. Expander devices, typically embedded into a system backplane (see
page 66 ), support
large configurations of SAS end devices, including SAS cards and SAS and SATA disk drives.
With expander devices, you can build large and complex storage topologies.
There are two types of SAS expanders: fanout expanders and edge expanders. Each performs a
different role in a storage system. (For more information about how SAS expanders work, refer
to the STA Web site at www.scsita.org.)
You can connect up to 128 SAS ports to an edge expander. (A single edge expander can
therefore support up to 128 SAS addresses.)
You can connect up to 128 edge expanders to a fanout expander.
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 next 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 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