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Chapter 1: So You Want to Use a Cluster
Overview
William Gropp
What is a "Beowulf Cluster" and what is it good for? Simply put, a Beowulf Cluster is a supercomputer that anyone can build and use. More specifically, a Beowulf Cluster is a parallel computer built from commodity components. This approach takes advantage of the astounding performance now available in commodity personal computers. By many measures, including computational speed, size of main memory, available disk space and bandwidth, a single PC of today is more powerful than the supercomputers of the past. By harnessing the power of tens to thousands of such low-cost but powerful processing elements, you can create a powerful supercomputer. In fact, the number 5 machine on the "Top500" list of the world''s most powerful supercomputers is a Beowulf Cluster.A Beowulf cluster is a form of parallel computer, which is nothing more than a computer that uses more than one processor. There are many different kinds of parallel computer, distinguished by the kinds of processors they use and the way in which those processors exchange data. A Beowulf cluster takes advantage of two commodity components: fast CPUs designed primarily for the personal computer market and networks designed to connect personal computers together (in what is called a local area network or LAN). Because these are commodity components, their cost is relatively low. As we will see later in this chapter, there are some performance consequences, and Beowulf clusters are not suitable for all problems. However, for the many problems for which they do work well, Beowulf clusters provide an effective and low-cost solution for delivering enormous computational power to applications and are now used virtually everywhere. This raises the following question: If Beowulf clusters are so great, why didn''t they appear earlier?Many early efforts used clusters of smaller machines, typically workstations, as building blocks in creating low-cost parallel computers. In addition, many software projects developed the basic software for programming parallel machines. Some of these made their software available for all users, and emphasized portability of the code, making these tools easily portable to new machines. But the project that truly launched clusters was the Beowulf project at the NASA Goddard Space Flight center. In 1994, Thomas Sterling, Donald Becker, and others took an early version of the Linux operating system, developed Ethernet driver software for Linux, and installed PVM (a software package for programming parallel computers) on 16 100MHz Intel 80486-based PCs. This cluster used dual 10-Mbit Ethernet to provide improved bandwidth in communications between processors, but was otherwise very simple—and very low cost.Why did the Beowulf project succeed? Part of the answer is that it was the right solution at the right time. PCs were beginning to become competent computational Appendix B. For the others, this book provides a solid background for understanding how to specify, build, program, and manage a Beowulf cluster.We begin by defining what a cluster is and why a cluster can be a good computing platform. Since not all applications are appropriate for clusters, Section 1.3 introduces techniques for estimating the performance of an application on a cluster, with an illustration drawn from technical computing. With this background, the next two sections provide two different ways to read this book. Section 1.4 provides a procedural approach, from choosing which components will constitute the cluster Section 1.5 provides a topical approach, such as how to program it, run jobs on it, or specify a cluster''s components.
