Archive for May, 2007

Fabric Mess, or how to do things right

Tuesday, May 29th, 2007

When a company is about to relocate to a new floor or a new building, that is the time when the little piles of dirt swept under the rug come back to hunt you.

In several companies I have been to, I have stressed the need of an ordered environment. This is valid to networking and hardware serial numbers as well as it is valid for FC hardware, but when it comes to FC, things always get somewhat more complicated, and when the fit hit the shan, the time you require for tracking down a single faulty cable, or a link led turned off is a time you need for other things.

I can sum it up to a single sentence – Keep you SAN tidy.

Unless you have planned your entire future SAN deployment ahead (and this can be planning ahead for years and years), your SAN environment will grow up. Unlike network, where short cable disconnections have only small influence on the overall status of a server (and this allows you to tidy up network cables on the fly after rush hours when traffic volume is low – without downtime), tidying up FC cables is a matter for a planned downtime, and let me see the high-level manager who would approve 30 minutes downtime (at least) with some risk (as there is always when changing cables) for "tidying up"…

So, your SAN looks like this, and this is the case, and this can be considered quite good:

Cables length is always an issue

You can track down cables, but it requires time, and time is an issue when there is a problem, or when changes are to take place. Wait – which server is connected to switch1 port 12? Donno?

The magic is, like most magic trick, non magical at all. Keep track of every cable, every path, every detail. You will not be sorry.

I have found out that the spreadsheet with the following columns would do the work for me, and I’ve been to some quire large SAN sites:

1. Switch name and port

2. Server Name (if server has multiple FC ports, add 0, 1, etc. Select a fixed convention for directions, for example – 0 is the leftmost, when you look directly at the back of the server). Same goes for storage devices.

3. SAN Zone of VSAN, if valid.

4. Patch panel port. If you go through several patch panels, write down all of them, one after the other.

5. Server’s port PWWN

On another spreadsheet I have the following information:

1. Server name

2. Storage ports accessible to it (using the same convention as mentioned above)

3. LUN ID on the storage described above.

If you keep these two spreadsheets up-to-date, you will be able to find your hands and legs anytime, anywhere in your own SAN. Maintaining the spreadsheet is the actual wizardry in all this.

Additional tip – If your company relocates to another building, and your SAN is pretty much fixed and known, hiring a person to manufacture by-the-length FC cables per device can be one of the greatest things you could do. If every cable has its own exact length, your SAN environment would look much better. This is a tip for the lucky ones. Most of us are not luck enough to either affort such a person, or to relocate with a never-changing SAN environment.