Adaptec 2268300R manual SAS Expander Connections

Appendix A: Introduction to SAS ● 93

Some backplanes support daisy-chain expansion to other backplanes. For example, you can daisy-chain (connect one to the next) up to nine Adaptec S50 enclosures to a single SAS card in a host system.

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 92), 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 including the fanout expander).

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 Domain
SAS	SATA
Disk Drives	Disk Drives
SAS	SATA

SATA

Edge

SAS Card

Expander

Edge

Expander

Edge

Expander

Disk Drives

SATA SAS

Fanout Expander

SAS Card

Edge Expander	Disk Drives
	SATA
SAS Card
Expander	SATA
	Disk Drives

SAS SATA

SAS SATA

Disk Drives

Disk Drives

Edge

SAS