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Dell SAN Foundations Online Training Course
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Index
Course Overview
SAN Introduction
SAN Architecture
Interface
Fibre Channel Concepts
Topologies

Hardware Components
Host Bus Adapters
Media/Connectors
Switches
GBICS
Storage Devices
Bridges
Tape Devices
Rack Mounting
Environmental Concerns

Software Components
LUN Masking
SAN Management
Data Management
Clustering

Section Review
SAN Implementation
Course Review
Course Feedback
Contact Dell

Fibre Channel

Fibre Channel Concepts

In the past decade, computer performance has substantially increased, along with the need for robust, highly available, and disaster-tolerant computing resources. As these resources are pushed to their limits, performance problems are often traceable to the I/O subsystems: the interface itself is not fast enough.

Parallel SCSI has been a market leader for over 15 years. Many SCSI devices are available and, because of the backward compatibility of SCSI, many older devices can still be used. However, one SCSI drawback is its relatively short bus length. Although the latest SCSI standards have addressed this, overall speed and reliability issues have caused storage engineers to look toward a new interface, Fibre Channel. Fibre Channel is the general name of an integrated set of standards developed by the American National Standards Institute (ANSI).

Fibre Channel was designed to be a serial interface, which relies on point-to-point "network type" interconnections. SCSI on the other hand is a bus that relies on channel communications. A channel also provides a direct or point-to-point connection between the communicating devices. Channels are typically hardware intensive and transport data at a high speed with low overhead.

Contrast this to a network, which is a collection of nodes (clients or servers) with its own protocol. A network has a relatively high overhead since it is software intensive; consequently, its performance is slower than that of a channel. A network can handle a more extensive range of tasks but is more prone to disruption caused by adding or removing nodes.

Fibre Channel combines the best elements of these two methods of communication into an I/O interface that meets the needs of both channel and network users.

Fibre Channel is simply a transport vehicle for the supported command set. Supported command sets include:

  • SCSI
  • Internet Protocol (IP)
  • ATM
  • Link Encapsulation
  • IEEE 802.2
Fibre Channel packs the data into frames and transports the information to the appropriate device. The encapsulated command set is responsible for data access.
Comparing Fibre Channel and SCSI
When Fibre Channel is compared to traditional SCSI, it's clear why it is the interface of choice in a SAN environment.

  This image creates a rounded corner Fibre Channel This image creates a rounded corner This image creates a rounded corner SCSI This image creates a rounded corner


Performance A serial interface that operates at 2 Gigabits per second. A parallel interface that operates up to 160MB a second.


Devices 126 devices using loops or up to 16 million with a switched fabric. 16 devices per SCSI channel.


Availability Allows addition or removal of devices without rebooting. Generally the host server must be rebooted to recognize new devices.


Cabling Can be either copper or fiber optic (or a combination of both), with lengths of 30m for copper and up to 10km for fiber optic. Only copper cable is supported, at lengths up to 25m.


Termination No termination is required. Termination is required.




Terminology
The fundamental elements of Fibre Channel connectivity are Nodes, Ports, and Links.

 Node
A node is a physical device, hard drive, host bus adapter, or storage processor, which has at least one N_Port. A node can have multiple N_Ports.

 Port
A port can be either the interface or the adapter board, either of which may connect the serial Fibre Channel signal with the parallel-based end device.

Port Types

  • N_Port - node port
  • NL_Port - node port on a loop
  • F_Port - fabric port
  • FL_Port - fabric loop port
  • E_Port - expansion ports
  • G_Port - generic (or universal) port

    •  Link
    The link is the optical or copper cable interconnecting two Fibre Channel devices. The link plugs into a port on either end.


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