[Freshman2022]

Hi,
I am going to build a new workstation for LES while the maximum cell count is no more than 30 million(mostly around 20 million). Without regard for license, I have made the following configuration(considering budget):
2 x AMD ROME EPYC 7542
16 x 8GB RAM(2R x 4,RECC,3200MHz)
H12DSI-N6 motherboard
1TB SSD & 4TB HDD
My questions are:
1. Is there any better solution especially for CPU (same budget please).
2. From the forum, it seems that base clock does not influence the speed much(i am not sure). Does it mean that I can choose a lower base clock CPU for saving budget.(older Naples EPYC 2x 32 Cores or...).
3. The memory bandwith bottleneck is a mainly problem for higher cores. So I am considering whether Rome EPYC 2 x 16 Cores (or Milan) is a better choice（cost-effective).
I will appreciate it if anybody can give some advice! Thank you very much!

[flotus1]

Cheapest offer I can find for these CPUs is ~2300€. That's an OK price for 32 Rome cores... but deals for Milan are already starting to show up: https://geizhals.eu/amd-epyc-7513-10...loc=pl&hloc=uk
Prices for the 24-core version are also in free-fall: https://geizhals.eu/amd-epyc-7413-10...loc=pl&hloc=uk
Side-note: those are probably two competing bots determining the prices, undercutting each other in regular intervals. Don't know why, but I find it quite funny.

You probably won't find any 8GB DDR4-3200 2Rx4. Those are all single-rank, you need at least 16GB DIMMs for dual-rank. You will either have to go 16x16GB, or use single-rank instead.

1. Is there any better solution especially for CPU (same budget please).

See above, I personally would prefer the newer generation. There have been some notable improvements, like running the IF at a 1:1 ratio even with DDR4-3200, and a single slice of L3 cache per chiplet.

2. From the forum, it seems that base clock does not influence the speed much(i am not sure). Does it mean that I can choose a lower base clock CPU for saving budget.(older Naples EPYC 2x 32 Cores or...).

Base clock is indeed pretty meaningless, the CPUs will never run at that speed. Don't buy Naples in 2022, it's really slow. Trust me, I know

3. The memory bandwith bottleneck is a mainly problem for higher cores. So I am considering whether Rome EPYC 2 x 16 Cores (or Milan) is a better choice（cost-effective).

Factoring in the cost for the rest of the workstation, the sweet-spot for price/performance is somewhere around 24 cores per CPU.
See e.g. my latest results in the OpenFOAM benchmark thread (2x Epyc 7543):

simpleFoam run times for 100 iterations:
#threads | runtime/s
====================
01       | 471.92
02       | 227.14
04       | 108.51
08       |  52.11
16       |  28.81
32       |  18.11
48       |  15.46
64       |  13.81

That's 12% performance gains between 24 and 32 cores per CPU. It's up to you to decide whether this is worth it to you, with the prices you pay.

[Freshman2022]

Thank you for your quick reply！It really helps me a lot.
I have seen your latest results in the OpenFOAM benchmark thread which is pretty good. But there are still some confused questions remaining:
1. Does the cell count affects the performance gains greatly? I mean maybe the performance gains will increase (or decrease) since the cell count increases and no longer 12% anymore (just a guess).
2. Actually I perfer Milan for i have heard that ROME's IFOP is only 1476MHZ which is only enough for 2933MHZ RAM. But the problem is that i can only afford ROME x2 or Milan x1 in my area. So which one should I choose while Rome x2 may have the twice memory bandwith and cores?
3. I have learned that your workstation is 2x AMD Epyc 7543, Gigabyte MZ72-HB0, 16x64GB DDR4-3200 (RDIMM, 2Rx4). I am wondering that does the L3 cache affect the speed a lot? While 2Rx4 is much more expensive than 2Rx8 RAM, I am confused whether 2Rx4 worths the price? And would you mind telling me why you choose Gigabyte MZ72-HB0 rather than H12DSI-N6 (better bios?).
I am very grateful for your professional reply!

[flotus1]

Does the cell count affects the performance gains greatly? I mean maybe the performance gains will increase (or decrease) since the cell count increases and no longer 12% anymore (just a guess).

I don't think there is a substantial difference in scaling with higher cell counts.

2. Actually I perfer Milan for i have heard that ROME's IFOP is only 1476MHZ which is only enough for 2933MHZ RAM. But the problem is that i can only afford ROME x2 or Milan x1 in my area. So which one should I choose while Rome x2 may have the twice memory bandwith and cores?

Definitely 2x Rome. The performance difference for the solver phase is not that big, the generational improvements are mostly nice-to-have for a workstation.

3. I have learned that your workstation is 2x AMD Epyc 7543, Gigabyte MZ72-HB0, 16x64GB DDR4-3200 (RDIMM, 2Rx4). I am wondering that does the L3 cache affect the speed a lot?

Yes, the larger L3 caches have an effect on performance. But not enough to justify the steep price increase when on a limited budget.
I had to make the same tradeoff when configuring this workstation. Milan-X was already available, but there was just no way to fit those into the budget.

While 2Rx4 is much more expensive than 2Rx8 RAM, I am confused whether 2Rx4 worths the price?

x4 or x8 doesn't matter, it is hard to even measure such small differences reliably. 1R vs. 2R is the important bit here. But it's the same tradeoff. When all you need is 128GB of RAM, buying double that amount just to get dual-rank DIMMs is rather expensive for a performance improvement in the order of 10%. You need to decide if it is worth it to you.

And would you mind telling me why you choose Gigabyte MZ72-HB0 rather than H12DSI-N6 (better bios?).

I heard good things about it: https://www.youtube.com/watch?v=6v6VdVXoNOs
It's a great board, I especially like that you can set actual fan curves via IPMI, and use slow-spinning fans out of the box. And the VRM design and cooling are less problematic in a workstation case. It's as close to a workstation board as we ever got for dual-Epyc.
What I didn't like is that there is virtually no support for Gigabyte enterprise products, at least in Europe. Might be different in other parts of the world, don't know.

All in all, configuring such a workstation is a constant balancing act of of spending just a bit more money for just another incremental performance bump.
Rome vs. Milan
16, 24 or 32 cores per CPU
single- vs. dual-rank DIMMs
The slightly more expensive Gigabyte board...
128MB, 256MB or even 768MB of L3 cache
Taking it all together, these increments do add up to quite a substantial difference in performance. But they also increase the price by a factor of 2-4x. With a limited budget, you have to draw the line somewhere.

[Freshman2022]

I don’t know how to express my gratitude for your professional reply because I have been suffering from tradeoff (poor budget ahah) for weeks. I am clear now after reading your reply and all your replies since 2020. My configuration is:
2 x AMD ROME EPYC 7452 (unless I can afford 2 x AMD Milan EPYC 7413)
16 x 16GB 2R x 4,RECC,3200MHz RAM (for future upgrades)
Gigabyte MZ72-HB0
1TB SSD & 4TB HDD
fanless power supply and two silent fans
Thank you Alex and have a nice day!

[flotus1]

If I can offer another piece of advice:
I consider fanless power supplies a waste of money, unless you are building an entirely fanless PC for whatever reason. With any decent quality power supply, you won't be able to hear the PSU fan over the other fans in the system.
Also don't skimp out on the case and case fans. The system will produce somewhere around 400W of heat during operation. That's a lot, and the more case fans you add, the quieter the system can be overall. And a case with good ventilation is also a must.

[Freshman2022]

Thank you for your advice!
Well that advice is quite useful for me and actually a new knowledge for me since i used to think that the more fans i add, the more noisy the system can be overall. I guess that may because the fans speed can be lower while adding more fans? But why the amount of fans do not increase the noise?
And by the way, I am wondering whether you mind telling me your choice for PSU, CPU fans and case fans because I think you are professional. ( I am pretty sorry for that I have troubled you so much)
Thanks again for your help!

[flotus1]

There are several reasons why more fans can lead to a quieter PC.
But let's get that out of the way fist: you are right, a PC with more fans CAN be louder. More fans spinning at the same rpm will always be louder. That's why fan speeds need to be adjusted.
Having more fans allows you to run them at lower rpm for the same amount of cooling. Let's take a hypothetical scenario where we replace 1 fan with 2 fans, and adjust the rpm to produce the same airflow: the 2-fan setup will be quieter.
Perceived fan noise isn't linear with rpm, and cooling isn't linear with airflow either.
You can take a look at the numbers Noctua puts on their product page for the NF-A12x25 PWM:
Screenshot_20220616_165832.png
The low-noise adapter drops the rpm from 2000 to 1700, which reduces airflow by 17%. But also reduces noise by 4dB(A).
Long story short: more fans can spin slower for the same amount of cooling, making them quieter overall.

I am wondering whether you mind telling me your choice for PSU, CPU fans and case fans because I think you are professional

For the power supply, Seasonic Focus PX 750 is pretty decent value in my opinion: https://geizhals.eu/seasonic-focus-p...loc=pl&hloc=uk
It is by far not the only choice you have. Any other name brand with similar specs will do fine. Just make sure it has TWO EPS 8-pin connectors. Most low- to midrange PSUs only have one of those. Note that these are different than 8-pin PCIe connectors.
My favorite case at the moment is the Phanteks Enthoo Pro 2: https://geizhals.eu/phanteks-enthoo-...-a2338821.html
It is on the pricey side, and comes without fans included. But they are decent quality with lots of cooling potential. And can be set up in a "bottom to top" airflow configuration. Which pairs nicely with Noctua CPU coolers for the SP3 socket. I recommend at least 4 case fans, 2 as bottom intake and 2 as top exhaust.
CPU coolers: Noctua NH-U14S TR4-SP3.

[Freshman2022]

Your support is greatly appreciated. I can not wait to assemble my new workstation while my old one needs 15mins for a time step sloving 22M cell in simple method hah.