How to troubleshoot SANs using WWN zoning

What you will learn from this tip: The benefits of WWN zoning, beyond ease of configuration.

Identifying devices by their World Wide Name (WWN) when setting up zones on a SAN makes configuration easier, but it also provides some maintenance and troubleshooting advantages over tying devices to specific ports on the SAN switch.

In general, zoning makes testing and maintenance easier because it divides the SAN into sub-networks. Each zone can be tested individually without interrupting processes running on devices attached to other zones. Beyond that, WWN zoning offers some important advantages when it comes to SAN management and troubleshooting.

The major troubleshooting advantage of WWN zoning in troubleshooting arises from the fact that you can move WWN-identified devices from port to port on the SAN easily.

There are a number of possible troubleshooting strategies. The most obvious one is to test the device is the problem, or whether the glitch is somewhere else in the fabric. Move the device to be tested to another port and see if the problem persists. If it does, the problem is probably in the device or somewhere between the port and the device.

Unfortunately most problems with SANs aren't as simple as a bad device. The majority of SAN problems involve some sort of degraded performance. This can be the result of anything from a misconfigured component to a subtle interaction between various parts of the SAN. Again, WWN zoning allows

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you to use a divide-and-conquer strategy to isolate the problem. By switching devices among ports you can test various combinations of load, topology and other factors to locate the offending parts of the SAN.

When working with a SAN using WWN zones, it is important to remember that each device has to be registered with the SAN by WWN before the SAN will recognize it. In fact, if the SAN has trouble recognizing a device, the WWN registration is usually one of the first things to check.

For more information:

Tip: Crash Course -- Zoning

Tip: Zoning, part 1 -- An overview of zoning

Webcast: SAN School, Lesson 3 -- What makes a SAN go

About the author: Rick Cook has been writing about mass storage since the days when the term meant an 80 K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last 20 years he has been a freelance writer specializing in storage and other computer issues.

This was first published in August 2004

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