How clouds and fibre has remade the data centre

Current state of the market

How should the coming changes in the data centre affect your plan? The first step is to determine how much of your traffic needs very low latency right now. If cloud computing, migrating critical storage or a new low latency application such as algorithmic stock trading is on the drawing broad, then it is best to start the move now to the new architecture. Most enterprises don't fall in that group yet but they will in 2010 or 2011 and thus have time to plan an orderly transformation.

The transformation can also be taken in steps. For example, one first step would be to migrate Fibre Channel storage onto the IP fabric and immediately reduce the number of adapters on each server.

This can be accomplished by replacing just the top of the rack switch. The storage traffic flows over the server's IP adapters and to the top of the rack switch which send the Fibre Channel traffic directly to the SAN. The core and end of rack switch do not have to be replaced. The top of the rack switch supports having both IP adapters active for storage traffic only with spanning tree's requirement of only one active adapter applying to just the data traffic. Brocade and Cisco currently offer this option.

If low latency is needed, then all the data centre switches need to be replaced. Most vendors have not yet implemented the full range features needed to support the switching environment described here. To understand where a vendor is; it is best to break it down into two parts. The first part is whether the switch can provide very low latency. Many vendors such as Arista Networks, Brocade, Cisco, Extreme, Force 10 and Voltaire have switches that can.

The second part is whether the vendor can overcome the spanning tree problem along with support for dual adapters and multiple pathing with congestion monitoring. As is normally the case vendors are split on whether to wait until standards are finished before providing a solution or provide an implementation based on their best guess of what the standards will look like. Cisco and Arista Networks have jumped in early and provide the most complete solutions. Other vendors are waiting for the standards to be completed in the next year before releasing products.

What if low latency is a future requirement, what is the best plan? Whenever the data centre switches are scheduled for replacement they should be replaced with switches that can support the move to the new architecture and provide very low latency. This means it is very important to understand the vendor's plans and migration schemes that will move you to the next generation unified fabric.

Layland is head of Layland Consulting. He can be reached at robin@layland.com.