i think you'll find that the PC cluster is more cost effective than the SP or other parallel machines built. an example: in our aerospace department we have two parallel machines one is an sgi origin with something like 24 processors which cost in excess of a million dollars (early 90s dollars) and is supported by a whole bunch of guys in the schools computer admin dept, we have a PC cluster with 50 PII/400 processors whic hcost 100K in 1994. i'm not certain which has the higher peak speed but they are quite close. the cluster runs linux and is supported by one grad student and is extremely stable. so you see for a given amount of money the workstation cluster gives more performance and for a given level of required performance the cluster costs less so it's better both ways. moreover as new stuff comes along you can retrofit easily.

have no fear about the stability our 50 processor cluster runs jobs anywhere from a few hours to several days (a friend of mine had molecular dynamics simulations that took a week at a time) and 160 MW is no problem. as for the pre and post processing i'd probably still go with an independent SGI as nothing comes close in handling graphics in my experience, but then all you'd need is one or two single processor indy's

here's apage you can check out for info on a running linux cluster http://cac.psu.edu/beatnic/Cluster/Lionx/index.html note however that this is a reasearch cluster and the people who put it together were very interested in measuring lots of things. you'll probably not do everything they did so you could be up and running faster and cheaper than they did also check out: http://cocoa.ihpca.psu.edu/ which is probably more typical of how people here would do things also peruse http://cac.psu.edu/beatnic/Cluster/ for links to more info. putting together a cluster is easier than you might think specifically http://bart.aero.psu.edu/cocoa/HOWTO/cocoa.html tells you how one cluster was put together

SMP and linux works fine here. There used to be issues in the early 2.2 kernels when using SMP and an IDE hard drive. But these have been fixed and linux is running smoothly and scales extremely well on a duo-proc. I haven't tested a quad but they have been reported to work very well with linux. For more than 4 CPUS however the scaling ain't as good, but then again, where will you find a PC with more than 4 cpus? ;-)

By the way, if you're wondering which hardware to buy for linux, just go to penguincomputing.com or valinux.com and see which hardware they give you when you buy a machine from them, and buy the same.

And no, linux's stability ain't a myth. This is the most stable OS I have worked with. Unless your hardware is defective, you should very rarely experience a crash. What confuses a lot of people is when the display 'freezes' suddenly. This ain't a crash, just a display freeze which can be fixed through networking. The OS underneath is still alive and kicking..

-bern

Thank you all for your input. It is been very helpfull. Could one conclude the following:

For parallel codes using domain decomposition, a PC/LINUX cluster is a very attractive alternative to existing parallel machine, because it is cheap and although it is a slightly slower than existing parallel machine today, in time one could throw away parts and buy new ones cheap, thereby increasing the performance/cost ratio.

Stability is no problem for the PC/LINUX cluster.

Finding a good supplier can be significant in the time used to get a PC/LINUX cluster running.

It is preferable to eiter have a systemmanager who is knowledgeable or to be (or become) a wizkid yourself (?).

For large and fast postprocessing purposes a workstation has proven to be a necessity.

Price of a PC: 2K. Price of HP workstation; 6K. What causes this difference? I assume the people at HP want to sell there workstations. From the information above, one can only conclude, that that might very well be a waste?

Thanks again,

Guus