Ultimate Machine Build - CFD

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Ultimate Machine Build - CFD - £3-5K Budget

Hi

I'm looking at spec'ing a machine for cfd (Ansys CFX). Looking for raw speed for mathematical calculation 12-16GB ram spec...£3,000-5000. Dont worry about graphics card as that'll be a quadrofx 3500

I'm a bit out of touch with the latest and greatest, can someone please help me spec a machine?

Thanks
morgan
 
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Hi

I'm looking at spec'ing a machine for cfd (Ansys CFX). Looking for raw speed for mathematical calculation 12-16GB ram spec...£3,000-5000. Dont worry about graphics card as that'll be a quadrofx 3500

I'm a bit out of touch with the latest and greatest, can someone please help me spec a machine?

Thanks
morgan

For raw floating point performance the i7 920 would be the best choice. Most high end boards will support 12GB of RAM. On that budget a dual quad core setup (Mac pro-style) would be a good option using high end Xeons
 
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You have a relatively difficult decision to make. The two current options are a desktop machine running an i7 processor somewhere around the 4.2ghz mark, or a workstation board running two processors at their stock speeds, which are likely to be around the 2.5ghz mark. It's hard to judge which will be quicker (how many threads is your code good for?), but the dual socket box will cost a lot more.

In the future a single socket six core processor will be out. I believe this is expected Q1 next year. It overclocks well based on what we know so far, and throws a third option into the ring. A single six core processor at 4ghz is likely to walk all over a dual socket board at 2.5 and cost less. No benchmarks, my reasoning is 6x4>8x2.5 and 12 threads is better than 16 if the application isn't carefully multi threaded.

This makes me lean towards a fairly conventional box with the six core processor replacing the four core one upon release. What time frame are you working with, will this machine be running 24/7, does it matter how much noise it makes and is raw performance more important than performance / £?

A final idea is that the cheaper single socket version may allow a better quadro and lead to conclusively better performance.

I almost don't envy you :)
 
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You have a relatively difficult decision to make. The two current options are a desktop machine running an i7 processor somewhere around the 4.2ghz mark, or a workstation board running two processors at their stock speeds, which are likely to be around the 2.5ghz mark. It's hard to judge which will be quicker (how many threads is your code good for?), but the dual socket box will cost a lot more.

In the future a single socket six core processor will be out. I believe this is expected Q1 next year. It overclocks well based on what we know so far, and throws a third option into the ring. A single six core processor at 4ghz is likely to walk all over a dual socket board at 2.5 and cost less.

This makes me lean towards a fairly conventional box with the six core processor replacing the four core one upon release. What time frame are you working with, will this machine be running 24/7 and does it matter how much noise it makes?

Saying that though, it might the case that 6 core Xeons are compatibale with current Xeon boards, which'll mean he could have a 12 core system in Q1 next year!:p
 
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Ah, very true. The argument for and against overclocking a very difficult one to judge when workstations are involved.

Do you get to assemble this yourself?

Totally agree. If he's stressing "mathematical calculations" personally I'd edge towards a dual CPU setup with error correcting memory over a clocked i7 with OTS RAM. The i7 may well out perform the dual Xeon on badly threaded apps but on a properly written application the dual CPU Xeon should shine through. Depending on how low level he wants to write his code there's even an outside argument for an itanium based setup :eek::p
 
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Does that software require paying per core, per CPU, per system or normal software license ?
I was looking to build one of these (for CFD) and couldnt decide between dual Xeon or overclocked i7. Found out the software was pay per CPU which kinda made the decision for me.
 
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That's all very well, but then again he could have dual CPUs? :p

The motherboard will be the problem though, ideally on that budget, I'd want a board with dual i9 compatible sockets, and preferably 8 DIMM slots, but I don't think such a board exists?

Have you contemplated water cooling? If you ran an SLI or Crossfire setup, you could have two loops, with a processor and a GPU on each loop?
 
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@Muel, X58 systems use triple channel memory. So not 8 ram slots. A quadro card is nvidia, the fx3500 is approximately equivalent to the 8800 gaming cards, and costs around £600. If there is the budget for two of them then a single card is likely to be a better choice, avoiding driver issues.

ECC might swing it. Some of the nehalam processors include error correcting mechanisms as well, previously only found in itanium systems.
 
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hi all

thanks for talking the time to respond. right, I'll try to answer all of the questions!

We do indeed pay per core. We have licences for up to 5 cores only - ie any more cores is a waste. (its cores too, not cpus)

Time scale..this week ideally. I've been given the red light at work...that doesnt happen often!

Noise etc...would be better if lower noise..watercooling?

Would prefer it if somebody else assembled but I've done it myself before, and there are plenty of people at work who could also do it.

Budget is £3000-5000 dont need a screen with that.


The way the software works is that a CFD study is broken into various stages:

Meshing>pre-processing/setup>Solver>post processing

Only the solver stage can use multiple cores, for meshing etc its all on one core so a fast (single core) is prefferred.

Regarding Xeons etc. I currently sue a Dell Precision T7500 with a single 8 core xeon @2.66Ghz cpu with 16GB ram. Its quick but not as fast as I would like. I was hoping that the i7's would be faster.

Any more input is really appreciated. hopefully this response helps!
 
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What's the ram utilisation like? Single socket i7 systems (which the 5 core limit strongly suggests) are capped to 12gb until 4gb sticks of ddr3 are readily available. So it becomes a question of whether raw cpu speed (which a single, clocked i7 has ludicrous amounts of) or amount of ram is more useful.

If 12gb will suffice things are simpler, a gigabyte UD5, 12gb corsair ram, i7 950 are probably the ones to base the machine on. In the future you can move to 24gb of ram and a true six core processor if needed.

Watercooling means it'll run faster, with less noise, but take longer to assemble. Overclocking with all six slots occupied is more difficult, so it may be worth contacting ocuk for this if you don't have a few days to spend on it. They've done customised watercooled builds in the past, I'm sure they'd be happy to do so again.

Otherwise you'll need to go down the HP/equivalent route again, where raw performance will be distinctly lacking in 5 thread programs compared to a clocked i7, and it'll cost you, but the aftersales support will be there.
 
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Hang on, will the HT make a quad count as 8 cores? I guess it counts on the software?

I'd go for an i7 975 on some kind of intercooled water cooling setup with that budget! Especially seeing as the graphics side of things won't have to be a high budget setup.
 
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Careful reading of the license documentation should clear it up - in my case it was per CPU. But as HT makes theoretical cores I wouldnt expect them to be counted. If they are you can just turn it off.

Do the 975's actually clock any higher ?
 
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