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Implement Fibre Channel over wide area networks.

Ponder these design considerations for a successful storage interconnect solution.

Fibre Channel, the high-performance interconnect, has become a major driving technology for storage networking applications. Emerging as a serious contender in the early 1990s, this industry-standard, high-speed serial data transfer protocol allows greater throughput over longer distances than other interface technologies, greater flexibility in connecting servers and storage, and high reliability.

The growth of storage area networks (SANs) is often attributed to the availability of Fibre Channel, due to its rapid data rate (100 Mbps) and ability to span 70 kilometers between nodes. Fibre Channel seems a natural fit for companies that want to send large volumes of data over longer distances, key requirements in storage networking.

While SANs can function within the local environment, their true potential lies in linking heterogeneous systems into cohesive networks on a wide scale. Therefore, companies will require wide area network (WAN) connections to link the Fibre Channel SAN islands across the enterprise. Matching Fibre Channel to wide-area technologies becomes a requirement to allow true global data access.

Implementation of Fibre Channel over WAN is not an all-or-nothing proposition. A phased implementation plan is possible, and assures that all steps along the way meet the organization's needs and conform to current and future standards.


The following checklist summarizes the major challenges and technical details that need attention during network design to successfully implement Fibre Channel over WANs. These "do's and don'ts" can help get your networking project off on the right foot.

Define the project goals. Is the project being undertaken to consolidate storage and save on costs, to streamline user accessibility, to add backup/restore capabilities, or to speed access to information? These goals will lead to the characteristics that are most important.

Determine the application characteristics. Will the application require synchronous or asynchronous information exchange? What are the I/O requirements of that application? What are the data throughput requirements? How much time is needed to accomplish the goal? How much redundancy is necessary?

Design the network for maximum efficiency. An important consideration is the speed mismatch between Fibre Channel and wide area telecommunications technology. Fibre Channel runs at 100 megabytes per second; circuits such as asynchronous transfer mode (ATM) technology operate at much slower speeds--in the 155-megabit range. Dealing with this bytes vs. bits speed mismatch requires looking at how flow control will be handled--by the server component, by the networking infrastructure or by the storage component, or a combination of all.

Determine your backup window. How much data do you need to back up, and how much time do you have? Between those two parameters, you can determine what the overall speed must be to move that amount of data. Add in a buffer factor, so it can recover in case of error. For example, if you have a four-hour backup window and 100 gigabytes of data, do the math and calculate how much bandwidth you need, which translates down to bits per second vs. bytes per second.

Design in a measure of redundancy. Redundancy is important, both for local and long-distance applications. Look at routing algorithms and how data can be rerouted and recovered; design out single points of failure in a solution set.

Design in as much transparency as possible. The goal should be to connect any network components and the network infrastructure together in a local and wide area environment, with network operations--such as error recovery and flow control--completely transparent to the application.


In designing your network, understanding the tradeoffs between the various telecommunications options is vital:

* Leased lines, a circuit-switched technology, offer bandwidths ranging from 1.54 Mbps with a T1 line, up to 45 Mbps for a T3 line. They provide a dedicated circuit, owned by the customer. The advantages here are centered on continuous availability, while the drawbacks include cost and requisitioning time. Atypical cost for a 500mile T3 circuit ranges from $15,000 to $30,000 per month.

* Cell- or packet-based services, such as ATM or synchronous optical network (SONET), allow higher scalable bandwidth. ATM data can flow over SONET networks, a ring topology especially prevalent in metropolitan areas. The provider sells access points into shared SONET ring, with the customer allotted a specific amount of bandwidth. Bandwidth is limited; if you exceed the bandwidth, you may be able to tap unused bandwidth, network traffic permitting. ATM bandwidth ranges from 45 Mbps to 622 Mbps. Typical costs for an equivalent T3 circuit may run between $6,000 to $13,000 per month.

* Internet protocol (IP) is a router network that can be connected across any distance, using either leased lines or ATM. Initial costs can be about the same as leased-line and ATM pricing. Most companies already have an IP network in place for other applications, such as e-mail. There is often unused bandwidth, or low periods of use that can be leveraged for storage applications.

The decision regarding your telecommunications choice is important because the wide area component is one of the largest investments in your network--a monthly, recurring cost. Check what the telco and/or networking vendors can do to maximize your investment. Specifically, look at their ability to compress data, which can provide several times the throughput for the same investment, allowing you to move more data faster, realize efficiencies and gain a greater return on investment. Compression can be accomplished on all lines, including IP.

Latency, or delay time, is another ever-present factor in a long-distance network. Latency--translating into a delay of one millisecond per 100 miles--is dependent on speed of light. Thus, the need exists to calculate the latency affected by distance, add that figure to the latency of components in the infrastructure and determine the total impact on the application. For Fibre Channel, channel extension techniques can be used to overcome distance and latency issues associated with wide area operations.


Wide area data communications can be complicated, often involving multiple public facilities. Data may be routed through several communications offices before reaching the appropriate destination, each location a potential point of failure. Therefore, an important factor in the introduction of Fibre Channel-over-WAN implementation is the use of networking products and services from suppliers with proven experience in both storage networking and wide area environments. Consider these few points:

* What is the vendor's experience with wide area connectivity? Experience in long-distance channel conversion over an ATM, for example, should be a "given."

* Look closely at the reliability of components that fit into the networking structure. What has the vendor designed into products to allow automatic recovery of linkage failure, and what does its rerouting algorithms provide?

* Looking at the products or the network function is not enough, however. Ask questions. What's the vendor's support philosophy? What's its recovery plan if one point goes out? What kind of tools does it have to figure out what the network problem is? Does it have diagnostic tools to troubleshoot circuits from any one of the carriers and determine if the problem is on the Fibre Channel or the circuit side?

* Equally important, is customer support available 24x7? Network problems keep no timetable, and service disruption cannot be afforded at any time. The name of the game today is high availability; settle for nothing less than round-the-clock network monitoring and quick problem resolution.

Extending Fibre Channel over any distance is poised to become the next important technological ability for storage networking. The inherent bandwidth in Fibre Channel make it the preferred technology for meeting the high-volume challenges of exploding data-storage requirements.

Larsen is director of product management for open systems at Computer Network Technology (CNT), Minneapolis, MN.

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Title Annotation:Industry Trend or Event
Comment:Fibre Channel, a high performance interconnect, is emerging as the industry dtandard for network storage applications.
Author:Larsen, Brian
Publication:Communications News
Geographic Code:1USA
Date:Sep 1, 2000
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