Remaking the data center

Low-latency switches are the foundation for building a unified-fabric data center

A major transformation is sweeping over data center switching. Over the next few years the old switching equipment needs to be replaced with faster and more flexible switches.

Ethernet switch vendors propose data center collapse

Three factors are driving the transformation: server virtualization, direct connection of Fibre Channel storage to the IP switching and enterprise cloud computing.

They all need speed and higher throughput to succeed but unlike the past it will take more than just a faster interface. This time speed needs to be coupled with lower latency, abandoning spanning tree and supporting new storage protocols.

Without these changes, the dream of a more flexible and lower cost data center will remain just a dream. Networking in the data center must evolve to a unified switching fabric.

Times are hard, money is tight; can a new unified-fabric really be justified? The answer is yes. The cost savings from supporting server virtualization along with merging the separate IP and storage networks is just too great. Supporting these changes is impossible without the next evolution in switching. The good news is that the switching transformation will take years, not months, so there is still time to plan for the change.

The Drivers

The story of how server virtualization can save money is well known. Running a single application on a server commonly results in utilization in the 10% to 30% range. Virtualization allows multiple applications to run on the server within their own image, allowing utilization to climb into the 70% to 90% range. This cuts the number of physical servers required; saves on power and cooling and increases operational flexibility.

The storage story is not as well known, but the savings are as compelling as the virtualization story. Storage has been moving to IP for years, with a significant amount of storage already attached via NAS or iSCSI devices. The cost saving and flexibility gain is well known.

The move now is to directly connect Fibre Channel storage to the IP switches, eliminating the separate Fibre Channel storage-area network. Moving Fibre Channel to the IP infrastructure is a cost saver. The primary way is by reducing the number of adapters on a server. Currently servers need an Ethernet adapter for IP traffic and a separate storage adapter for the Fibre Channel traffic. Guaranteeing high availability means that each adapters needs to be duplicated resulting in four adapters per server. A unified fabric reduces the number to two since the IP and Fibre Channel or iSCSI traffic share the same adapter. The savings grow since halving the number of adapters reduces the number of switch ports and the amount of cabling. It also reduces operational costs since there is only one network to maintain.

The third reason is internal or enterprise cloud computing. In the past when a request reached an application, the work stayed within the server/application. Over the years, this way of design and implementing applications has changed. Increasingly when a request arrives at the server, the application may only do a small part of the work; it distributes the work to other applications in the data center, making the data center one big internal cloud.

Attaching storage directly to this IP cloud only increases the number of critical flows that pass over the switching cloud. It becomes critical that the cloud provide very low latency with no dropped packets. A simple example shows why low latency is a must. If the action took place within the server, then each storage get would only take a few microseconds to a nanosecond to perform. With most of the switches installed in enterprises the get can take 50 to 100 microseconds to cross the cloud, which depending on the number of calls adds significant delays to processing. If a switch discards the packet, the response can be even longer. The only way internal cloud computing works is with a very low latency and non-discarding cloud.

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