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Network World - The eternal challenge of the data center is balancing the quality of the user experience against the economics of building and operating the data center. One of the most significant trends today is the use of infrastructure virtualization to improve the economics.
Specifically, by virtualizing, pooling, and sharing compute, storage, and network resources across multiple applications and users (a.k.a. "building clouds"), the average utilization can be dramatically improved. Virtualizing servers may improve average utilization from 5% to as much as 60% or 70%. Resource pooling may also increase the agility of the business. New applications or services can be brought online in minutes or hours rather than the weeks or months that are normally required when new physical infrastructure needs to be ordered and installed. And as user demand shifts, resources can be dynamically reallocated to maintain a high quality of user experience.
One of the underlying realities of clouds or shared resource pools is that larger clouds and more dynamic clouds enable greater efficiency and flexibility. Unfortunately the desire for greater scale and dynamism places significant pressure on the data center network. It is the network or networks that interconnect the resources and enable the creation of a cloud. No network, no cloud. Unfortunately, networks are also the greatest impediment to success, as most networks today are not architected to support the scale or dynamism demanded by the modern data center. Only by re-architecting the data center network can we realize the full benefits of virtualization and cloud computing.
The typical architecture for a data center Ethernet network employs a tree structure, arrayed in three layers of switching, fanning out from the core. This design was derived from the architecture of the LAN and was adopted in data centers approximately 10 to 15 years ago when Ethernet displaced SNA, token ring and DEC-Net. As the data center evolved over the last 10 years, the network began to exhibit shortcomings, including suboptimal performance, inherent inefficiency, and excessive complexity. None of these shortcomings is trivial, but it is the complexity that truly stands in the way of the virtualized data center.
The complexity arises from the fundamental architecture of the tree structure. Networks are comprised of multiple, autonomous switching devices that cooperate through shared protocols. Managing a network entails managing not only the switches but also the interactions between the switches.
As a network scales up in capacity, the number of switches in the network scales in a relatively linear fashion. However, the potential interactions between the switches scale up dramatically, as a function of the square of the number of switches. This can be expressed using the formula i = n*(n-1)/2, where i is the number of potential interactions, and n is the number of managed devices. This geometric increase in the number of interactions to be managed drives the complexity of the network, inhibiting the benefits of virtualization.