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Old   August 1, 2016, 09:04
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Hi, I am trying to get a workstation to run OpenFoam. My budget is $4000, and so fat I am looking at ECC memory and Xeon processors. Could you offer any feedback on the following build?

Memory: 32Gb 2400Mhz ECC (8*4Gb or 4x8 - I think 8x4 would be better for multi core?)
Video: NVIDIA Quadro K620 2GB
Processor: 2x Xeon E5-2630 v4 (25Mb cache - 2.2Ghz core speed - 68.3 Gb/s max mem. bandwidth)

My concerns: Each processor has 10 cores, which would put me on 20 cores total. This would definitely be good for simulations where I could use multiple cores. My simulations include a great deal of turbulence modeling and fine meshing, and I was told multiple cores can help when modeling turbulence, not sure if this is a correct statement, or incomplete; you know how grad students are, the repeat what they hear. Heck I am doing it too... Anyway, The processors have hyperthreading, but I would turn this feature off. The bad part, 2.2 Ghz power per core... so, if my simulations require more individual core power than multi-core performance, this wouldn't be good. Another concern is 20 cores for a 32Gb RAM machine is probably not ideal, so if I really wanted to take advantage of 20 cores, I would have to go much higher on RAM (motherboard has 12 DIMM slots - BUT processor has a max of 4 mem channels.).

Any help appreciated, thx.

Last edited by eangola; August 1, 2016 at 10:08.
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Old   August 2, 2016, 00:46
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Hi eangola,

E5-2630 v4 does not support your 2400Mhz. Its supports only DDR4 1600/1866/2133.

Reference Link for E5-2630 v4:
http://ark.intel.com/products/92981/...Cache-2_20-GHz

E5-2630 v4 is a good processor but 32GB is very low memory (3.2 GB per core).
I recommend 64 GB per processor socket (16GB X 4). In total 128 GB per node.
Since you have 20 cores in total this will give you 6.4GB per core which is good for the computation.
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Old   August 2, 2016, 04:06
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Get a motherboard with 16 DIMM slots and at least 8*8GB of RAM to start with. Or even better 8*16GB if you can afford it, RAM is not really expensive these days. This way you make sure to use the full potential of your CPUs which requires at least 4 DIMMs per CPU and you can still upgrade RAM later if necessary.
It is true that your processor only supports up to DDR4-2133. However, depending on the price difference which is usually very small I would still recommend DDR4-2400 just in case you want to upgrade the CPUs later.
Edit: if you are confused about the number of DIMM-slots not matching the amount of memory channels... one memory channel can be occupied by more than one DIMM -typically 2 or 3 DIMMs per channel- and still operate with full memory bandwidth as long as the channels are occupied symmetrically. The opposite is not true: in order to get the maximum memory bandwidth possible, you need at least one DIMM per channel which is why 4*8GB is not advisable. On the other hand, 4GB DDR4-DIMMs are always single-ranked which also has a slight negative impact on performance.

Don't worry about the 2.2GHz base frequency. The turbo frequency for all cores which is always used provided adequate cooling is 2.4GHz. Single-core performance is not as bad as you might think it is, with only one or two active cores, the processor will run at 3.1GHz. See this page for more information:
https://www.microway.com/knowledge-c...ep-processors/
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Old   August 2, 2016, 08:44
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Quote:
Originally Posted by flotus1 View Post
Get a motherboard with 16 DIMM slots and at least 8*8GB of RAM to start with. Or even better 8*16GB if you can afford it, RAM is not really expensive these days. This way you make sure to use the full potential of your CPUs which requires at least 4 DIMMs per CPU and you can still upgrade RAM later if necessary.
It is true that your processor only supports up to DDR4-2133. However, depending on the price difference which is usually very small I would still recommend DDR4-2400 just in case you want to upgrade the CPUs later.
Edit: if you are confused about the number of DIMM-slots not matching the amount of memory channels... one memory channel can be occupied by more than one DIMM -typically 2 or 3 DIMMs per channel- and still operate with full memory bandwidth as long as the channels are occupied symmetrically. The opposite is not true: in order to get the maximum memory bandwidth possible, you need at least one DIMM per channel which is why 4*8GB is not advisable. On the other hand, 4GB DDR4-DIMMs are always single-ranked which also has a slight negative impact on performance.

Don't worry about the 2.2GHz base frequency. The turbo frequency for all cores which is always used provided adequate cooling is 2.4GHz. Single-core performance is not as bad as you might think it is, with only one or two active cores, the processor will run at 3.1GHz. See this page for more information:
https://www.microway.com/knowledge-c...ep-processors/
Thank you! very informative.
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Old   August 2, 2016, 08:46
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Quote:
Originally Posted by mdgowhar View Post
Hi eangola,

E5-2630 v4 does not support your 2400Mhz. Its supports only DDR4 1600/1866/2133.

Reference Link for E5-2630 v4:
http://ark.intel.com/products/92981/...Cache-2_20-GHz

E5-2630 v4 is a good processor but 32GB is very low memory (3.2 GB per core).
I recommend 64 GB per processor socket (16GB X 4). In total 128 GB per node.
Since you have 20 cores in total this will give you 6.4GB per core which is good for the computation.

Thanks! 6.4GB per core should be great
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