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Explain Your Boss Advantages Of PC Clusters...



Summary

PC clusters now offer solution for affordable supercomputing. The role of traditional supercomputers (like CRAY) was once taken over by workstations. Now the huge PC market allowed unprecedented dynamics of PC hardware evolution. Good PC offers far the best price/performance ratio unavailable with any workstation. Todays networking technology made PC clusters feasible computing tool and allowed them to beat other technologies also in absolute numbers. The third major factor is explosive growth of free software enabled by global Internet. Worldly collaboration became well established and very productive paradigm of software engineering even for the most demanding tasks like writing the whole UNIX operating system. Releasing all the source code made global testing possible and for important programs raised the standards of software quality to level hardly achievable by any company.

This new situation attracted attention of many groups with a need for high performance computing. PC clusters became well recognized and practical supercomputing tools and they are being succesfully built and used at universities and research sites all over the world.

In the near future we can expect wider use of PC clusters in the industry: Thought the PC cluster architecture was designed to achieve top computing power, it also has a potential to serve as a redundant failproof system.

However promissing, the PC cluster technology is still new and not known to general public. To harnes its power, decision makers need to be well informed about its benefits and its pitfalls. Probably the most scarce resource in this domain is nor the hardware nor software but knowledgeable system administrators. Acquiring one and creating optimal conditions for his work and sustained selfeducation might well be the major factor.

PC cluster - What Is It?

It is a group of (for example 16) personal computers connected by a very fast network. Dislike usual personal computers, cluster members have no individual displays, no keyboards, even maybe no floppy disks. They do have fast processors, enough RAM, hard disks and fast network cards. Fast switch is used for network interconnect.

Computers run Linux operating system - free implementation of UNIX. Standard Linux itself provides enough to make the cluster usable. On the top of it, standard parallel programming tools can be installed, yielding portability of programs between PC clusters and traditional supercomputers. Some minor operating system improovements special for PC clusters also exist.

Alltogether, PC clusters architecture is similar to the one of nowaday supercomputers, but it employs widely used components only (albeit their usual use is different). This ensures good component quality and low (or even zero) price.

Three Times More For The Same Money

Thought direct comparisons with commercial solutions are difficult and do require exact specification of tasks to be solved on the computers being compared, it can be estimated that for scientific work you will get at least three times better performance with PC clusters than you would get using any commercial workstations or supercomputers of equivalent price. Even ratios as high as 10 or 15 are not uncommon as a result of these comparisons.

Commodity Well Known Hardware

Supercomputing PC cluster is composed of usual PC hardware. Switch used for PC interconnect is a normal network component (but usually it is being used in central parts of big networks only). Thus the price can be much lower than the price of any specialised supercomputing hardware. Thought technically speaking PC hardware is not "the best possible", market considerations make it optimal.

Components are chosen from the best ones on the market, however the very top (like the fastest processors available in limited amounts) is better avoided bacause of unreasonable price. It is better to buy more of next-to-top parts instead.

Easy Hardware Service

PC hardware is well known. Many sites can manage instant service by replacing faulty parts themselves. Otherwise there always is a lot of service companies to choose from.

Free Software

Most of the software needed is free of charge, including source code. This includes complete re-implementation of UNIX operating system, networking, graphical X-windows system, editors, compilers, various scientific tools etc. (Example of free software known to general public is TeX.) Software piracy not needed anymore.

Free Software May Be MORE Reliable

Serious scientific experiments proved that important freely available software (GNU utilities) is considerably more stable than equivalent software produced by any commercial UNIX vendor, including the most respectable international companies. This is probably due to the fact that free software available with source code is debugged by all the world's people (instead of just one company). And futhermore, authors of widely used free software are usually excellent programmers.

Free Software Is Flexible

Free availability of all the source code makes it possible to modify any part of your system.

Free Software Is Ideal For Education

Every piece of the software source code may serve as invaluable source of knowledge - nothing is hidden in compiled programs.

Not Dependent On One Company

All the components are commodity. Should one company fail to deliver it, there always is another.

Low Risk

Should you ever find that this solution is not good for your purpose, you can still use the hardware as ordinary individual PCs. Your investment does not involve the risk of buying promissing but too specialised and not suitable hardware.

There Is Really No Display? How Is It Used???

Users can connect to the cluster via network using any graphical X-terminal. For this purpose one can use another PC, old workstation, or it is possible to put graphics to the cluster itself.

Who Is Able To Work On PC Cluster?

First of all, users should be able to use UNIX operating system. Good and cheap way to become familiar with UNIX is to install Linux on a single PC. For many users this is nearly all what is needed. Programmers who would like to learn more (and get more) could start with PVM.

How much does it cost?

Typical number seemes to be $50,000 for a 16-node cluster. The number is relatively constant in time - later on it is optimal to use better parts, the performance is higher, but not the price. Of course, all this is just blatant simplification, you can make cluster with 8 nodes or 64 nodes...

Is PC Hardware Really So Powerfull?

Yes, it is. Sometimes you just cannot see it because it is being used with not so good software. But however bad some operating systems might be, there is also positive side of this: Slow software forced hardware improovements to compensate for this, and millions of users were forced to make huge hardware investments. Those suffering users financed unprecedented PC hardware boom. Now you just have to choose good operating system (e.g. Linux).

Another factor is workstation manufacturers' advertisement. For sure they will not tell you that workstation era is over. They will rather let you think that powerfull people can be recognised as users of their workstations.

The Future

PC clusters may become standard for scientific computing. The number of sites using this type of machines is growing rapidly, and building and using PC clusters is becoming easier with every new instalation - majority of cluster administrators is willing to share their experience and new software tools they develop.

Big Warning For The Very End

Once again I must repeat - get good system administrator. There is still a piece of adventure in using PC clusters and deep knowledge and daring are more important than amount of money spent for hardware.

And one more warning regarding PC hardware. There is excellent PC hardware but this is not to say that all PC hardware is good. In fact choosing the right PC hardware for your cluster requires knowledge of the hardware itself, wide knowledge of the hardware market and also detailed information about hardware support provided by Linux operating system. Consult well informed hardware specialist before you buy.



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