Adaptec 1430SA, 58300, 44300 How Do SAS Devices Communicate?, What’s a Phy?, What’s a SAS Port?

Appendix A: Introduction to SAS ● 59

How Do SAS Devices Communicate?

SAS devices communicate with each other through links. A link is a physical connection between two phys.

As shown in the following figure, SAS devices contain ports which contain phys (see next section), and each phy contains one transmitter and one receiver (one transceiver). A phy can belong to one port only.

SAS Device

Narrow
	Phy	Receiver
Port		Transmitter
SAS Device
	Phy	Receiver
Wide		Transmitter
Port	Phy	Receiver
		Transmitter
	Phy	Receiver
		Transmitter
	Phy	Receiver
Wide		Transmitter
Port	Phy	Receiver
		Transmitter
	Phy	Receiver
		Transmitter

link

SAS Device

		Narrow
Transmitter	Phy
Receiver		Port
Transmitter	Phy
Receiver		Wide
Transmitter	Phy	Port
Receiver
SAS Device
Transmitter	Phy
Receiver
Transmitter	Phy
Receiver		Wide
Transmitter	Phy	Port
Receiver
Transmitter	Phy
Receiver

What’s a Phy?

Phys are part of the physical communication connection between SAS devices. Each phy contains a transceiver that sends data back and forth between SAS devices.

When a connection is formed between two end devices, a link is established from a phy in one port to a phy in the other port. As shown in the figure above, a wide port can support multiple independent links simultaneously.

Phys are internal, within SAS connectors (see page 60).

SAS cables physically connect one or more phys on one SAS device to one or more phys on another SAS device.

What’s a SAS Port?

Note: Because the physical link between SAS devices is from phy to phy, rather than port to port, a port is more of a virtual concept, different from what is normally considered a port on other types of RAID controllers and storage devices.

A port is one or more phys. A narrow port contains one phy. A wide port typically contains four phys.

Each port has its own unique SAS address (see page 60), and all the phys in a port share that same SAS address.