[bindesboll]

My company has aproved an upgrade of our CFD licenses to ANSYS CFX to enable 32-parallel processing. So I am about to configure a hardware solution to utilize up to 32-cores. As the cost of HPC licenses is high relative to the hardware my focus is on getting the highest performance out of the 32-parallel processes. I will be running cases up to 10-40 mio. cells., oil spray combustion with radiation. Based on my initial investigations I came up with a system consisting of 2 PCs of 16 cores connected to a mini-cluster. The cost for a master node in a rack system is relatively high for such a small system.

2 pcs PC:
Dual CPU Xeon E5-2670 (8 cores)
8 x 4 GB RAM, 1600 MHz (2 set of 4 memory channels) = 32 GB
HDD: 250 GB, 7200 rpm for Windows
One of the machines will be with 1 TB 10,000 rpm SATA-600 for CFD files.
Interconnect for mini-cluster: 1 Gigabit or faster
Interconnect from mini-cluster to user workstation (Pre/post): 1 Gigabit

My questions regarding this configurations:

1) I expect the performance of the individual PCs to be limited by memory bandwidth. So it might be a waste of money to go for higher speed CPUs. But which CPU fits the available memory bandwidth: E5-2690, 2687W, 2680, 2670, 2667, 2665 or 2660?
I can tell their SPECfp_rate from: http://www.spec.org/cpu2006/results/rfp2006.html
- but that might not tell what their performance is in practice if memory bandwidth is the bottle neck?

2) My ANSYS reseller has done the attached performance benchmark on a similar system. The decrease in scaling from 16 to 32 cores indicate that the applied 1 Gigabit cluster interface is limitting the performance. Thus I would like to know how fast (transfer rate and latency) an interconnect I need to have full scaling from 16-32 cores. I guess if the speed of the interconnect resemples that of the RAM, then increased speed would not gain performance? Anyone who has experience on this or can refer to results?

3) How fast disks would you recommend? Currently I am running SSD, which still takes a few minutes to load a large case i CFX-pre. But I dont know if this is disk speed limited. My plan so far is 1 TB 10,000 rpm disks in RAID 0. Pre/post will be running on local workstation (1 Gigabit connection) but using the files on the cluster.

4) A lot of people on this forum prefers i7. However, then I would need 5 PCs to get 30 cores - which would even increase the requirements for a fast cluster interconnect and most likely decrease the scaling further. Moreover the i7 doesnt seem to compete with the fastes Xeon E5 on raw single CPU performance:
http://www.cpubenchmark.net/high_end_cpus.html

I would really appreciate you input on my questions above!

Best regards
Kim Bindesbøll