De-mystifying Grid Technologies

Continued from page: 1

Tuesday, April 03, 2007

Grid Vs Cluster computing

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In a grid environment, we have a loosely coupled architecture of systems connected majorly over a Wide Area Network or an Internet. The job is more or less the same as is done by a Computational Cluster, which is to harness resources of multiple ideal machines. But in case of a Grid it's not necessary that it will only leverage the processing power of all the machines. You can instead create a Data Grid which actually creates and manages distributed data storage and is also called a Grid.

The other key feature of a Grid which actually differentiates it from a Cluster is its de-centralized model, where you generally don't have a controller in place and each and every node works independently. In this case the nodes can also be heterogeneous in terms of Operating Systems hardware architecture.

One example of grid computing is the infamous SETI@home project to search for extraterrestrial intelligence. There is a centralized telescope which captures radio signals from space and then transfers the data captured in small packets to several million computers connected to the Internet. The nodes then process these packets of data in their idle time and return the results back to a data center. This way high processing power is
obtained, utilizing the idle time of several computers spanning across the globe.

In this example you can clearly see that the architecture is completely de-centralized and loosely coupled. And is also very highly heterogeneous because over the Internet one can't control which OS or architecture will a node be using.

Clusters on the other hand use a single server or controller to manage and distribute/aggregate the processes and one or more client nodes connected via a tightly coupled environment such as a high speed LAN or some specialized high speed interconnect such as Myranet, etc. But, unlike grid computing, where each client computer can run its own OS, this one is controlled and managed by a single OS running across the computers in the cluster, making it highly homogeneous in nature. The server provides various files to clients for execution. Applications are run on clients using parallel processing algorithms.

The clients are just dumb terminals, with no display in most of the cases or input devices connected to them. The server is the single interface for the entire system, where all input and output takes place. To the user the entire setup appears as a single system. These formations of clusters are commonly known as SSI or Single System Image.

Beowulf clusters, which are built from commodity 'off the shelf' computer parts running free OSes like Linux, are an example of such a kind of cluster. They provide very cost-effective parallel processing.

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