Fibre Channel Basics

PC Institute

What is Fibre Channel?

Fibre Channel is a high speed communications method for attaching devices to a server (host) or groups of hosts.• Very high speed -1Gb/sec-2Gb/sec• Used mainly to connect to storage devices

- Can support non-Fibre Channel devices through gateways

• Also supports IP over fibre• Uses light to carry signals• Highly reliable connections• Very little signal interference

Fibre Channel Structure

Layered approach to data communications

Physical layer

Encode/Decode

Framing protocol/Flow control

Common services

Protocol mapping layer

Application

FC-4

FC-3

FC-2

FC-1

FC-0

Physical Fibre Channel Characteristics

FC Type Max Dist Optic Cable

Mode

SW: short-wave Fibre Channel

1Gb – 500m

2Gb – 300m50 micron

Multimode1Gb – 300m (175m)

2Gb – 150m (175m)62.5 micron

LW: long-wave Fibre Channel

10 km (6 miles) 9 micron Single mode

50 or 62.5 microns

Short wavelength, multimode. Waves interfere with each other; short wavelengths cause more signal loss.

Long wavelength, single mode. No interference with other signals; less signal loss.

9 microns

Fibre Channel Terms

Node• A node is the source or destination for information being

transported.

Port• A port is a hardware entity within a node that performs data

communications over the channel.

Link• A link is a connection between two Fibre Channel ports

consisting of a transmit and receive fibre.

Fabric• The fabric is the means by which the Fibre Channel connects

devices.

Fibre Channel Addressing

Fibre Channel fabric uses a 24-bit address.• Allows for up to 16 million ports in a single configuration.• Addresses are assigned dynamically at login and do not

require any settings of switches or jumpers.• When logging onto a switched fabric, the address is assigned

by the fabric.• When connection is point to point, one of the two will assign

the other its address.

Arbitrated loop uses a different addressing scheme.• 127 addresses on loop.• When in an arbitrated loop, the loop address is assigned

during the loop initialization process (LIP).• The acronym for arbitrated loop physical address is AL_PA.

Point-to-point Fibre Channel

Point-to-point Fibre Channel is a direct connection between two devices.• Requires compatible port transmitters and receivers• Simple to implement• Dedicated bandwidth

Fibre Channel

Device

Fibre Channel

DevicePo

rt

Po

rt

Fibre Channel Arbitrated Loop (FC-AL)

Multiple devices are daisy-chained together• Ports are normally connected through a hub• Arbitration scheme determines which device controls the

loop• Offers full-duplex communications

- Performance impacted by number of devices

Fibre Channel Device

Fibre Channel Device

Fibre Channel Device

Fibre Channel Device

Port

Po

rt

Port

Po

rt

FC-AL Close-up With Devices

Repeatersat Each Hub Port

Server

CascadeLink

EmptyPort

RetimingCircuitry

at Each Node

1 2 3 4 5 6 7

Fibre Channel Switched Fabric

Flow of information is controlled by routers or switches instead of hubs• Scalable, robust design• Cost effective only in multi-node environment• Point-to-point connection between two devices• Multiple pairs of devices can communicate simultaneously

Fibre Channel Device

Fibre Channel Device

Port

Port Port

Port

Fibre Channel Device

Fibre Channel Device

Channel Co-existence with Other Technologies

Non-Fibre Channel devices cannot connect directly to Fibre Channel.• Requires a “gateway” device

- Provides physical cabling conversion- Provides protocol conversion

Fibre Channel Device

Gateway

Fibre Channel Device

Fibre Channel Device

Port

Po

rt

Port

Po

rt

Non-Fibre Channel Device (e.g. SCSI and SSA)

When to Deploy Fibre Channel

ServeRAID

ServeRAID

Windows2000

Linux

NovellNetware

UNIX