[maksins]

I went through the threads and general hardware recommendations, but could not find answer to my questions, so I am posting here.

I am getting a workstation with dual socket EPYC 7443 processor. The motherboard has 16 DIMMs.
As I understand, I should have at least 1 DIMM/stick per channel for balanced performance. Since it is dual EPYC, I have 16 memory channels, so I was inclined to get all 16 DIMMs filled.
My vendor is telling offering me 8 x 32 GB 3200 MHz dual channel memory sticks. I requested 16 x 16 GB 3200 MHz, but he says if I use all 16 DIMMs, my memory may operate at lower frequencies (e.g., 2666 MHz).
I would primarily use this workstation for FEA (LS-DYNA) and AUTODYN.

I have three questions:
How much of performance different would be in terms of 8 x 32 GB vs 16 x 16 GB?
Would dual channel RAM mean that effectively I should fill X/2 DIMMs for X memory channels?
Is it true that if I fill all 16 DIMM slots then memory may operate at lower frequencies?

Please share your insights.

[flotus1]

How much of performance different would be in terms of 8 x 32 GB vs 16 x 16 GB?

Hard to put a number down, it depends on a lot of factors. But you should not listen to the advice from this vendor. Not populating all memory channels makes no sense at all.

Would dual channel RAM mean that effectively I should fill X/2 DIMMs for X memory channels?

No idea how "dual-channel" came into this. There is no such thing as dual-channel RAM. Maybe they meant dual rank???

Is it true that if I fill all 16 DIMM slots then memory may operate at lower frequencies?

That should not be a thing with third gen Epyc CPUs. And even if memory transfer rates dropped down to DDR4-2933, the performance loss from that is still much lower than leaving half of all memory channels unpopulated.

Overall, pretty bad advice from your vendor. Which is a common occurrence unfortunately.

[aparangement]

Motherboard supermicro's H11dsi?

I heard another version, says all 16 DIMMs would down clock to 2933.

Turns out NOT true, at least not for BIOS versions later than August 2021, runs 3200 out of the box.

I did manually down clocked the RAM from 3200 to 2933, actually almost the same performance, due to better timings I guess.

But I guess 2667 would be too low to keep same level of performance, even with better timings.

Originally Posted by maksins

I went through the threads and general hardware recommendations, but could not find answer to my questions, so I am posting here.

I am getting a workstation with dual socket EPYC 7443 processor. The motherboard has 16 DIMMs.
As I understand, I should have at least 1 DIMM/stick per channel for balanced performance. Since it is dual EPYC, I have 16 memory channels, so I was inclined to get all 16 DIMMs filled.
My vendor is telling offering me 8 x 32 GB 3200 MHz dual channel memory sticks. I requested 16 x 16 GB 3200 MHz, but he says if I use all 16 DIMMs, my memory may operate at lower frequencies (e.g., 2666 MHz).
I would primarily use this workstation for FEA (LS-DYNA) and AUTODYN.

I have three questions:
How much of performance different would be in terms of 8 x 32 GB vs 16 x 16 GB?
Would dual channel RAM mean that effectively I should fill X/2 DIMMs for X memory channels?
Is it true that if I fill all 16 DIMM slots then memory may operate at lower frequencies?

Please share your insights.

[maksins]

Thank you @flotus1 and @aparangement for the answers.

Originally Posted by aparangement

Motherboard supermicro's H11dsi?

He said Gigabyte, so the only SP3 motherboard I know is Gigabyte MZ72-HB0.
Now, I have asked him for 16 x 16 GBs. He said prices may go up a little as 32 GB Reg server memories have better availability. I said ok, it is unlikely that I would invest in 8 x 32 GB to utilize all 16 DIMMs in future, it may be just be better to get a new system.

Any suggestion on CPU cooling for this kind of system? I would be using this as a desk Workstation with 4U tower Stand-alone/Pedestal Server chassis.
I don't want too much of noise, I enquired about liquid cooling and the vendor said it may cost north of $1500 to install liquid cooling with this. I am thinking Noctua NH-U14S TR4-SP3 Air Cooler. Any other recommendation for Air Coolers are welcome.

[aparangement]

Sorry I didn't notice it's 7003.

For 7003 I have no experience at all. (I would say it is less likely for 7003 board to have such strange behaviour, but who knows.. It's too expensive to actually buy one and test.)

Maybe you could ask for another model? Supermicro's H12DSI should also be available now. But still, better make it clear that you would return the machine if the RAM gets down clocked.

Originally Posted by maksins

Thank you @flotus1 and @aparangement for the answers.


He said Gigabyte, so the only SP3 motherboard I know is Gigabyte MZ72-HB0.
Now, I have asked him for 16 x 16 GBs. He said prices may go up a little as 32 GB Reg server memories have better availability. I said ok, it is unlikely that I would invest in 8 x 32 GB to utilize all 16 DIMMs in future, it may be just be better to get a new system.

Any suggestion on CPU cooling for this kind of system? I would be using this as a desk Workstation with 4U tower Stand-alone/Pedestal Server chassis.
I don't want too much of noise, I enquired about liquid cooling and the vendor said it may cost north of $1500 to install liquid cooling with this. I am thinking Noctua NH-U14S TR4-SP3 Air Cooler. Any other recommendation for Air Coolers are welcome.

[flotus1]

All right, here is the deeper dive:
Reduced maximum memory transfer rates have become less common, or at least less pronounced with modern systems. And even if the official spec (which is surprisingly hard to get a hold of) dictates reduced speed for some memory configurations, it is often possible to just overwrite that setting in bios. So that's reason 1 not to worry about it.
Looking at what actually could lead to reduced memory speed gives us reason 2: It is about the number of memory ranks per channel. The single value for maximum supported memory transfer rates (DDR4-3200 in this case) is for 1 rank per channel. Meaning if you populate all 16 memory channels with a single-rank DIMM, you are still guaranteed DDR4-3200. Even with 2 ranks per channel, I find it highly unlikely that Epyc Milan official spec would be lower than that. And it would definitely be possible to set it to DDR4-3200 anyway. What happens with 4 ranks per channel might be debatable, but with the amount of memory we are talking about here, this is irrelevant anyway.
And lastly reason 3, which I already discussed in my first post: dropping memory transfer rates a bit is still much better than just leaving half of all memory channels unpopulated.

Any suggestion on CPU cooling for this kind of system? I would be using this as a desk Workstation with 4U tower Stand-alone/Pedestal Server chassis.
I don't want too much of noise, I enquired about liquid cooling and the vendor said it may cost north of $1500 to install liquid cooling with this. I am thinking Noctua NH-U14S TR4-SP3 Air Cooler. Any other recommendation for Air Coolers are welcome.

A 4U form factor will negatively impact noise for several reasons. The limited space only allows for small CPU coolers. E.g. a Noctuas NH-U14S won't fit.
What's worse, most 4U cases lean more towards servers than workstations. Which means loud case fans, and sometimes even server-class power supplies with tiny 40mm fans that will drive you crazy within minutes.
Water cooling for the CPUs won't help with that. So if you value a quiet system, the case is a big factor to consider.