Dense wavelength division multiplexing for disaster recovery


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DWDM can transport multiple protocols

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Application assessment
The most important information to come out of a SAN assessment where a long-distance SAN link is a goal should be the very real data characteristics of all applications slated to throw data to the remote location, both now and in the foreseeable future. A few questions you should ask your application owners are:

  • How important is the data?
  • How much data is involved?
  • How many server connections (present and future) are anticipated?
  • What kind of data access (small asynchronous or large synchronous blocks) needs to be provided?
  • How will data be transported (Fibre Channel and/or IP)?
  • When will the data be accessed?
  • What are the availability requirements of that access?

These are all important questions that you must pursue and answer as honestly as you can, without just filling in the blanks with guesses. Involve senior management to remedy conflicts, such as a case of two or more application owners believing that their data adds the most value to the corporation.

By answering the above questions, you will be systematically eliminating or including specific vendors' offerings. For example, by determining that there are in fact varying levels of importance regarding the data that will flow over the long-distance SAN link, you may discover that QoS functionality is required within your connecting equipment. Continuing down this path, the answer to how much and what type of protocol data could very well steer you toward a DWDM solution and away from point-to-point leased dark fiber.

And by analyzing the size and frequency of data access evident in your applications, you will discover whether Fibre Channel (FC) or IP is best suited to provide you with the bandwidth and distance that your applications need and at the best possible price. Armed with this information and your application availability requirements, your staff will be in the best possible position to narrow choices between vendors, and thus reduce the possibility of being sold extraneous equipment.

In provisioning a long-distance SAN link, hone in on the scalability of that link in terms of capacity and performance. Laying optical cable is costly, so you want to spend more time crunching numbers than it takes to actually lay the cable. This extra effort may save you time and money by minimizing the possibility of fiber exhaust.

Possibly somewhat less important than scalability is the ability to support QoS and multiple protocols. Not all organizations require QoS or support for multiple protocols (such as FC, ESCON, IP and ATM). However, if during your application assessments you discover a real need and not simply a want for these features, you may want to start your ROI justification as soon as you finish reading this article. Although there are many benefits to be had--consolidation being one of them--the hardware products that support these features also require the deepest pockets. Specifically, if you fit into this category, you'll want to look at DWDM.

This was first published in September 2003

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