H11DSi-NT and octal channel memory

yorkman

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If I'm understanding the Supermicro manual for this motherboard correctly the only way I can get octal channel memory with dual epyc 7742 cpu's is to populate ALL 16 dimm slots with ram as long as the ram is 2666MHz or less (only 8 DIMMs can be used with 3200MHz).

Can someone confirm if this true? Because what I'd really like is to get only eight 2R modules @ 3200MHz (2R is better than 1R) if it will still give me octal channel memory and best performance.

Page 31 of the manual (https://www.supermicro.com/manuals/motherboard/EPYC7000/MNL-2027.pdf) seems to suggest only one channel per slot and so 8 modules would not give me octal channel memory, but I'm not 100% sure.
 

alex_stief

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With two Epyc 7742, you have a total of 16 memory channels. There is no other way than using 16 DIMMs if you want "octa-channel" on both CPUs.
Ranks per DIMM has nothing to do with it. With only 8 DIMMs, the best you could do is quad-channel on each CPU.
But let's be real: when dropping around 15k$ on CPUs, there should be a budget for 16 DIMMs.

The manual you linked is old: Release Date: July 27, 2018
So the memory speeds listed are for Epyc Naples.
 
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yorkman

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With two Epyc 7742, you have a total of 16 memory channels. There is no other way than using 16 DIMMs if you want "octa-channel" on both CPUs.
Ranks per DIMM has nothing to do with it. With only 8 DIMMs, the best you could do is quad-channel on each CPU.
But let's be real: when dropping around 15k$ on CPUs, there should be a budget for 16 DIMMs.

The manual you linked is old: Release Date: July 27, 2018
So the memory speeds listed are for Epyc Naples.
That's the only manual Supermicro has, straight from their website: H11DSi-NT | Motherboards | Super Micro Computer, Inc.

Thanks for confirming there's no other way to get octal channel memory. They do have a "Tested Memory List" at the link above but the smallest listed for the Rome cpu is 32 GB and 16x32GB is serious overkill for me because for what the system will be doing 24x7x365 it will never ever need more than 128 GB. They have more tested memory in 8 and 16 GB sizes but those are for Naples and Supermicro has not been able to confirm if they'll work with Rome too. I don't want to spend another $2 or $3K on top of $15K since many places don't accept returns.
 

alex_stief

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You will have to get at least 16 GB DIMMs. To the best of my knowledge, these are the smallest DDR4 RDIMM that come in dual-rank flavor. At least for DDR4-3200.
Looking at their tested memory list, they actually have what you need: 16GB DIMM, dual-rank, DDR4-3200: Memory List | Supermicro
 

yorkman

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@alex_stief If I go with 3200MHz ram then I can only fill 8 dimm's (it tells you this under Features) which means it won't give me octal channels. And if I go with 16x16 GB 2666MHz dimms then it may not work because this ram is only tested with Naples not Rome and I won't be able to return the ram if I buy it -:( This is the problem.
 

alex_stief

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I must insist on a screenshot of the passage you have in mind.
Since this is the first time I hear about this limitation, I still think there is a misunderstanding.
 

yorkman

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Just open the link here:

Key Features
1. Dual AMD EPYC™ 7001/7002* Series Processors (*AMD EPYC 7002 series drop-in
support requires board revision 2.x)
2. 2TB Registered ECC DDR4 2666MHz SDRAM in 16 DIMMs
4TB Registered ECC DDR4 3200MHz SDRAM in 8 DIMMs (Board revision 2.x required)
 
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IamSpartacus

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I think they just haven't updated their documentation. The manual doesn't even mention DDR4 3200 RAM.
 

yorkman

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I don't think they update the manual at all - they just update the product page and anything they've tested (RAM).

If you look at this Gigabyte page link you can see that being able to use 3200MHz in 8 DIMM's or less is common but not more than 8 DIMMs. And this link (Under "Get the Memory Performance Edge" heading) makes sure that you know that with Gigabyte you can now use 3200MHz across all 16 DIMMs since it's supported even with 2 DIMMs per channel while other brands do not.

So I'm pretty sure the SuperMicro motherboard won't work with 3200MHz on more than 8 DIMMs especially since they specifically say this. Also the manual on page 31 does suggest it's only one DIMM per channel hence we have to use all 16 DIMMs for octal channel memory. But with the Gigabyte board 3200MHz will still give you octal channel memory since it works at 2 DIMMs per channel. Would love to get this board if they sold it for dual Epyc cpu's, at least without getting a whole chassis which costs a LOT more.
 
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alex_stief

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And I would be willing to bet 50 bucks that it does. These "official" specs are always very conservative.
For example with Epyc Naples, the maximum memory spec with dual-rank DIMMs was DDR4-2400, according to AMD. And yet you can run DDR4-2666 without any issue.
 

IamSpartacus

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And I would be willing to bet 50 bucks that it does. These "official" specs are always very conservative.
For example with Epyc Naples, the maximum memory spec with dual-rank DIMMs was DDR4-2400, according to AMD. And yet you can run DDR4-2666 without any issue.
I agree. They also support a lot more types of RAM than what they list. They will always only list what they've manually tested themselves.
 

alex_stief

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Let's take a different angle and assess your options:
I guess you want maximum memory performance, otherwise you would not opt for dual-rank DIMMs. By extension, you also want all memory channels filled. And you also want the maximum possible memory speed.

So buying only 8 DIMMs is not an option anyway. And neither is buying slower than DDR4-3200.
The worst that could happen is that you have to down-clock memory to DDR4-2933. Still not the worst deal, at least you get better memory latency in return: https://forums.servethehome.com/index.php?threads/epyc-rome-ifop-limited-to-1467mhz.27113/

So with a lack of other options and -in my opinion- a very slim chance that 16xDDR4-3200 is actually incompatible, the decision should be rather easy.
 
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yorkman

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Ok, so you're saying I should just go with any 16 dual rank modules of 3200MHz @ 16 GB even though there aren't any that Supermicro tested successfully? If 16 don't work then down-clock them and if that still doesn't work sell them (at a lower cost) and try other brand of 2666MHz that's on their Naples list.

Still one problem though. I'm looking now and I don't see any 16 GB 2R 3200MHz RDIMM ram on eBay and I certainly want to avoid the Nemix ram. Only ones I found are 2666MHz that are 2R.
 

IamSpartacus

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Ok, so you're saying I should just go with any 16 dual rank modules of 3200MHz @ 16 GB even though there aren't any that Supermicro tested successfully? If 16 don't work then down-clock them and if that still doesn't work sell them (at a lower cost) and try other brand of 2666MHz that's on their Naples list.

Still one problem though. I'm looking now and I don't see any 16 GB 2R 3200MHz RDIMM ram on eBay and I certainly want to avoid the Nemix ram. Only ones I found are 2666MHz that are 2R.
I use these.

Hynix 16GB DDR4 3200 MEM-DR416L-HL01-ER32 Server Memory
 

yorkman

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Yes thanks. I was going to update my post...that's the only one I could find but the cheapest I found is $200 each...16 x $200 (plus shipping, duty/broker fees) will be $3300 CAD at minimum (closer to $3500 after all said and done)! That's out of the question for me...No way I want to spend $3500 just for ram. It took me a few years to save up $14,000 just to buy the cpu's, mobo, case, coolers, psu. I planned to spend no more than $1700 at my door for ram. Man. And I thought I'd be ready to order everything this weekend.

It seems like the most cost-effective option left is to just buy 16 x 8 GB 1R which is much cheaper, unfortunately at the cost of losing dual rank :-(
 
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alex_stief

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Not sure if similar tools exist for the rest of the world, but it sure would help you find better sources than ebay for new components.
Speicher mit Art: RDIMM mit ECC, Typen: DDR4, Speichertakt: 3200MHz, Rank: dual Preisvergleich geizhals.eu EU
16GB DDR4-3200 dual-rank start at around 90€, which equates to 132$ CAD.

dual rank modules of 3200MHz @ 16 GB even though there aren't any that Supermicro tested successfully?
They have this type of memory on their tested memory list.

then down-clock them and if that still doesn't work sell them
That won't happen.
 

yorkman

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Man. I didn't know getting 16x16GB, 2R @ 3200MHz RDIMM was going to be so difficult. Seems like my only choice is to go through one of 3 shady looking european sites (only 3 for 16GB, the rest are 32GB). Not sure this is where I want to send $2000 and hope I get what I ordered. And if there's some issue oh boy. Good luck. I do however appreciate the link. Tried googling those models but no luck finding anything in North America for a decent price.

UPDATE: There does seem to be a lot more of 1Rx8 (single rank) but I wonder how much performance I'd lose by not going with 2R.
 
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yorkman

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Guys. What if I just got eight 16GB dual rank 3200MHz RDIMMs? Would that give me octal channel memory or do I still need all 16 RDIMMs?

The reason I ask is because in my dual E5-2696v3 I have octal channel memory using single rank memory (1R) populating all 8 RDIMMs. So wouldn't I get octal channels too if I went with eight 2R (instead of 1R) RDIMMs?
 

sno.cn

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You need 16 sticks to populate 16 memory channels (8 channels per CPU). 8 sticks gives you 8 channels. Split that between two CPUs, and you're running quad channel on each CPU. 1R vs 2R doesn't change that.

I got better performance using single rank DIMMS in mine. Maybe it depends on what you're doing with it.

If you only need 128 GB, why not grab some 8 GB sticks from eBay.

The SM tested RAM shows hardly anything. You can use memory selector on Crucial's website and they'll show a bunch of options. There are many many memory sticks that work in this board. I tested a ton of RAM in my H11DSi on Rome and didn't have any compatibility issues.
 

yorkman

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You need 16 sticks to populate 16 memory channels (8 channels per CPU). 8 sticks gives you 8 channels. Split that between two CPUs, and you're running quad channel on each CPU. 1R vs 2R doesn't change that.

I got better performance using single rank DIMMS in mine. Maybe it depends on what you're doing with it.

If you only need 128 GB, why not grab some 8 GB sticks from eBay.

The SM tested RAM shows hardly anything. You can use memory selector on Crucial's website and they'll show a bunch of options. There are many many memory sticks that work in this board. I tested a ton of RAM in my H11DSi on Rome and didn't have any compatibility issues.
I was trying to get 2R since most people and websites say 2R gives better performance. When I was building my dual E5-2696v3 system a chess friend say it's better to use 1R but I don't remember now if he was speaking generally or specific to chess. I will be using it for chess and if you say 1R is faster for you then perhaps it depends on the program like you said. In computer chess cpu horsepower is most important but we use hash (ram) too for reading/writing the best moves/lines that it stores there. So memory performance is also important.

Thanks for that info. After all my attempts of finding optimal memory without breaking the bank have failed I think after reading your message the option is clear. It's a lot easier to find sixteen 8 or 16 GB 1R 3200MHz or lower dimms for a decent price.