Grids are not clouds and clouds are not grids, although most clouds reside on some form of grid infrastructure. That's that standard explanation you hear from vendors trying to convince you of the merits of their latest offerings.
But what, exactly, does that mean in the real world? If you're an enterprise manager with a specific problem to be solved, how do you know whether you need a cloud or a grid?
As with any evolving technology, nailing down exactly what clouds and grids are and what they are supposed to do can be difficult. Often, by the time one mindset becomes common, vendors and the user communities are halfway to redefining the technology for entirely new purposes.
So for what it's worth, I thought I'd gather up some of the current thinking on grids and clouds and try to at least find out what types of functions are suited to which platform.
Over at Websphere, Paul Wallis offers a helpful guide on the history of grid and cloud technology. Initially, grids were an extension of cluster computing, with the main hurdle being to define "data residency" to allow servers to access data wherever it was on the network and, by extension, allow users to tap into computing resources the way we tap into electricity. The cloud, which came of age with Amazon's Simple Storage Service (S3), combines grid technology with the SaaS approach to offer computing services over the Web on a commercial basis.
Still, part of the problem in delineating the difference between grids and clouds is that the problems they are supposed to solve aren't very obvious, according to Appistry VP Sam Charrington. Can both be used to address things like scalability, resource sharing, external hosting? Maybe, but taken to their lowest common denominators, grids generally provide scaled-out applications across multiple computers, while clouds bring in concepts like utility delivery models and Internet scalability. But those are just the very basic notions behind what is likely to be a very diverse set of capabilities.
For some, the difference between grids and clouds rests largely on how resources are made available to clients. Terremark Worldwide recently converted its Infinistructure utility computer platform into the Enterprise Cloud, in which clients purchase a set number of dedicated CPU cores and storage. According to Gartner analyst Lydia Leong, this differs from Sun and Oracle grids that charge by the minute for resources that are shared among all users.
Still others claim that the main difference will be the specific markets that grids and clouds appeal to. Tech blogger Irfan Habbib sees grids as more application-specific than clouds, and largely appealing to the scientific community in the fashion of the Open Science Grid (OSG) and the Enabling Grid for E-Science (EGEE). Clouds will likely find more commercial uses because they allow small businesses to get up to speed without a lot of upfront investment.
So, there you have it. Clouds and grids fully explained in a few short paragraphs. For my next trick, I'll enlighten you on life, the universe and everything.