LCDP at Sheridan
   over a high-speed network
General Cluster Information
Posted on December14, 2001


What makes a cluster different than a network of Workstations?

The main difference revolves around security issues, application software, administration, booting, and file systems. As delivered most Linux distributions have very high security enabled (for good reasons). This security often "gets in the way" of cluster computing.

The cluster consists of two or more Linux boxes connected through a Fast Ethernet switch (A hub will also work, but it is slower). One node is usually a gateway that connects to a local LAN. The gateway node is often the "login node" which has a keyboard, monitor, mouse and hard drive. The rest of the nodes could be "diskless"(no hard drive) and "headless"(no keyboard, mouse, or monitor) and often referred to as "computer nodes".
The following diagram describes the general setup:

Cluster schema




What are the basic kinds of clusters?

Clusters of computing systems come in two basic kinds. A cluster is uniform if all of the processors are the same. A cluster is heterogeneous if the computers are connected by a high-speed network, but the processors are different or use different operating systems.
Beowulf clusters are an example of the first kind clusters with a uniform set of systems running the same operating system. An example of the second kind is the heterogeneous set of supercomputers at SDSC, running HP, Intel, IBM, and Cray systems all on the same site. Controlling this environment is much more difficult than a uniform cluster. For instance, job-submission software must handle the different OS interfaces, character sets, and the different order of bits (bits are counted right to left or left to right) in the computer as well as different word lengths.
Meta clusters are clusters of clusters. The meta cluster is usually a group of clusters that are geographically distributed, nationally or around the world, but can be treated as a single resource by some very advanced software. Meta clusters also come in uniform and heterogeneous types.



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