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In this simplified representation, the servers at the top of the figure must access data on the storage devices in
the lower part of the figure. The A54812-SW switch manages the SAS configuration, allowing both servers to
access all storage devices. Or, if zoning is used, single application servers can access specific storage devices
exclusively.
You can connect multiple A54812-SW switches in various topologies to provide failover support and to increase
the number of connected devices in the SAS domain. The theoretical upper limit of SAS devices in a domain is
16,000. The upper limit of SAS addresses in an A54812-SW switch topology is 1000.
The following figure shows a high-level block diagram of the A54812-SW switch.
Figure 3 Block Diagram of the A54812-SW Switch
Brief descriptions of the A54812-SW functional blocks follow:
LSISAS3x48 Expander
– This block includes management functions such as routing, device discovery, and
zoning. It also includes the SDM firmware. This block controls the flow of data through the SAS connectors.
SAS Connectors –
The A54812-SW switch has 12 x4 Mini SAS HD connectors, numbered 0 through 11. It
supports connection to SAS devices at link rates of 12.0Gb/s, 6.0Gb/s, and 3.0Gb/s.
Ethernet Phy –
The external 10/100 Ethernet port provides access to the SDM management application, which
sets up storage configurations in the SAS domain, monitors the status of the switch, and runs diagnostic tests. It
also provides access to the SDM command line interface (CLI).
Fans –
The A54812-SW switch enclosure contains three fans. The fan speed can be monitored using the SDM
utility.
Flash Memory –
The LSISAS3x48 expander connects to a parallel flash memory through the expander’s
external memory interface. This flash memory is used for firmware storage and execution, as well as nonvolatile
data such as Ethernet MAC address and SAS World Wide Identifier (WWID).
Temperature Sensors –
The temperature sensors inputs can monitor with the SDM utility .
1.3 SAS Phys, Ports, and Connectors
Phys and ports are a basic concept of SAS. A phy is the basic physical connection point for a SAS device. A phy
contains a single transmitter and receiver, which communicate across a SAS link to a single transmitter and
receiver in another phy, as the following figure shows.
Figure 4 Link between Two Single SAS Phys
