Proware DP-503-F4A3, Installation And User Manual

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DP-503-F4A3 RAID SUBSYSTEM
18 Installation and User Manual
A topology defines the interconnection scheme. It defines the number of devices that can be
connected. Fibre Channel supports three different logical or physical arrangements (topologies)
for connecting the devices into a network:
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Point-to-Point
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Arbitrated Loop(AL)
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Switched (Fabric)
The physical connection between devices varies from one topology to another. In all of these
topologies, a transmitter node in one device sends information to a receiver node in another device.
Fibre Channel networks can use any combination of point-to-point, arbitrated loop (FC_AL), and
switched fabric topologies to provide a variety of device sharing options.
Point-to-point
A point-to-point topology consists of two and only two devices connected by N- ports of which are
connected directly. In this topology, the transmit Fibre of one device connects to the receiver
Fibre of the other device and vice versa. The connection is not shared with any other devices.
Simplicity and use of the full data transfer rate make this Point-to-point topology an ideal
extension to the standard SCSI bus interface. The point-to-point topology extends SCSI
connectivity from a server to a peripheral device over longer distances.
Arbitrated Loop
The arbitrated loop (FC-AL) topology provides a relatively simple method of connecting and
sharing resources. This topology allows up to 126 devices or nodes in a single, continuous loop
or ring. The loop is constructed by daisy-chaining the transmit and receive cables from one
device to the next or by using a hub or switch to create a virtual loop. The loop can be self-
contained or incorporated as an element in a larger network. Increasing the number of devices
on the loop can reduce the overall performance of the loop because the amount of time each
device can use the loop is reduced. The ports in an arbitrated loop are referred as L-Ports.
Switched Fabric
A switched fabric a term is used in a Fibre channel to describe the generic switching or routing
structure that delivers a frame to a destination based on the destination address in the frame
header. It can be used to connect up to 16 million nodes, each of which is identified by a unique,
world-wide name (WWN). In a switched fabric, each data frame is transferred over a virtual point-
to-point connection. There can be any number of full-bandwidth transfers occurring through the
switch. Devices do not have to arbitrate for control of the network; each device can use the full
available bandwidth.
A fabric topology contains one or more switches connecting the ports in the FC network. The
benefit of this topology is that many devices (approximately 2-24) can be connected. A port on a
Fabric switch is called an F-Port (Fabric Port). Fabric switches can function as an alias server,
multi-cast server, broadcast server, quality of service facilitator and directory server as well.
1.4.3 Basic Elements