Modern storage management software makes a storage administrator's life a lot easier, but it is no substitute for a methodical approach when something goes wrong with the SAN. Generally the best principle is to maximize your results by eliminating as much of the decision tree as possible at each step.
The best way to do this is to think before you act. Have you made a recent change in your setup? It's always a good idea to check first on the last thing you did. If it was working before that change, and it isn't working now, then that last change could very well be the culprit.
Then, if that doesn't offer a solution, the best place to start in tracking down a problem with your SAN is in the middle -- with the SAN switches and the rest of the fabric. This isn't because the switches are more prone to failure, but because the switches see both the storage and server sides. By checking the fabric first, you can usually narrow the problem down to either the storage or server sides, pruning the rest of your troubleshooting-decision tree by half.
You can continue this process to further subdivide the tree and zero in on the problem area with the minimum number of steps and wasted effort. Generally you will be able to narrow down your list of possible problems in short order.
Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.
This was first published in January 2003