Dot Hill Systems II 200 FC service manual FC Protocols, FC Topologies, Fibre Hubs and Switches

1.4.1FC Protocols

Two common protocols are used to connect Fibre Channel (FC) nodes together:

■Point-to-point—The point-to-point protocol is straightforward, doing little more than establishing a permanent communication link between two ports.

■Arbitrated loop—The arbitrated loop protocol creates a simple network featuring distributed (arbitrated) management between two or more ports, using a circular (loop) data path. Arbitrated loops can support more nodes than point-to-point connections can.

The FC, SATA, and SATA SE arrays support point-to-point and arbitrated loop protocols. Select the protocol you prefer by setting the desired Fibre Channel Connection Option in the Configuration parameters of the firmware application. For more information, see “Summary of Array Configuration” on page 5-1.

1.4.2FC Topologies

The presence or lack of switches establishes the topology of an FC environment. In a direct attached storage (DAS) topology, servers connect directly to arrays without switches. In a storage area network (SAN) topology, servers and arrays connect to an FC network created and managed by switches.

Refer to the SANnet II 200 FC and SATA Array Best Practices Manual to see information about optimal configurations for site requirements.

1.4.3Fibre Hubs and Switches

A storage network built on a Fibre Channel architecture might employ several of the following components: Fibre Channel host adapters, hubs, fabric switches, and fibre- to-SCSI bridges.

■Fibre hubs

An arbitrated loop hub is a wiring concentrator. “Arbitrated” means that all nodes communicating over this fibre loop share a 100-megabits-per-second (Mbps) segment. Whenever more devices are added to a single segment, the bandwidth available to each node is further reduced.

A loop configuration allows different devices in the loop to be configured in a token ring style. With a fibre hub, a fibre loop can be rearranged in a star-like configuration because the hub itself contains port bypass circuitry that forms an internal loop inside. Bypass circuits can automatically reconfigure the loop once a device is removed or added without disrupting the physical connection to other devices.

■Fabric switches.

1-12SANnet II 200 FC, SATA, and SATA SE Array Installation, Operation, and Service Manual • March 2005