SAN consolidation with director-class switches


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Advanced capabilities equal higher cost

Fibre Channel switches and directors generally aren't purchased directly from the manufacturer but through a server vendor, storage vendor, system integrator or VAR. Pricing will vary depending on a number of factors, including your relationship with your supplier. Director pricing can get expensive, not only for the hardware but for some of the license keys. Per-port costs for fully loaded directors are higher than same port count fully loaded fixed-port switches, in the neighborhood of 2:1 or more, but you can scale up better with directors; directors also have more high-availability features built in.

For some data centers, available power is an issue as their electric power utility companies have indicated that they can't bring in any additional power to handle peak workloads. In these cases, data centers are clamoring for more energy-efficient equipment. Like most IT equipment vendors, switch and director vendors are focusing on energy efficiency. Given the ability of directors to consolidate the workloads of several or more regular switches, the case can be made that a move to directors will yield power conservation benefits, so you can expect director vendors to emphasize their "green" features.

Do you need a director?
Before replacing your current switching infrastructure with a director, you need to determine your requirements. If you need any of the following, then you should consider

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a director-class switch:

  • High availability in each component of the Fibre Channel infrastructure
  • High port count
  • High total bandwidth
  • Lower percentage of ports dedicated to ISLs

You'll have to do some technical analysis to determine your specific needs, but if any of your requirements point to one or more of the above, then a director might be good solution.

The trade-offs between using directors and smaller, fixed port-count switches affect your equipment budget and operating budget. Directors are more expensive, but provide more features, as described previously. But you also need to consider the day-to-day management of your Fibre Channel infrastructure. Are you spending too much time managing too many "things"? Would it be easier to manage one large unit rather than several small units?

You should also consider if your storage infrastructure is in a growth mode, and if you'll need to add quite a few more ports now and in the near future -- and all in the same SAN. If so, a director's ability to add ports fairly easily might be a good option. If the additional ports you need were configured with smaller, fixed port-count switches, you should also account for the ports that would have to be dedicated to ISLs rather than to storage devices and servers.

As noted, if you do opt for one or more directors, you may still be able to use the smaller fixed-port switches that the directors are replacing. You could use those small switches as edge switches placed close to the servers or storage systems in a simple core-edge topology. You could also use the small switches to create a standalone testing environment.

Generally speaking, there are two good reasons to deploy switches and directors from the same manufacturer. First, the manufacturers are more likely to guarantee that the equipment is fully compatible with their own equipment. Secondly, you've probably already invested time, experience and money in training and getting comfortable with one brand of switches, so it will be easier to adapt to directors that have a similar look and feel rather than going through the time and expense of learning new equipment.

Directors can be very effective additions to your SAN, especially as you build for the future, but you'll have to carefully examine the features and pricing to ensure that they're the best solution for your shop.

BIO: Dennis Martin has been working in the IT industry since 1980, and is the founder and president of Demartek, a computer industry analyst organization and testing lab.

This was first published in April 2010

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