EPYC 7002 memory

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elag

Member
Dec 1, 2018
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hi
I am looking to build an Epyc system (probably 7302P or a 7282) on a Supermicro H11SSL-i board. I have some doubts about the memory:
I am planning on 128GB for now, preferably easily expandable.
8*16G is more expensive than 4*32. 4*32GB now gives me the option to expand later. How much performance will I loose when I go for 4DIMMs instead of 8? the new EPYC should loose less performance with 4 channels instead of 8 than the old ones, right?
And second: on the memory list the is the M393A4K40CB2-CTD (2666). I assume that the M393A4K40CB2-CVF
(2966) is suitable for EPYC?
 

Patrick

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Dec 21, 2010
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It is not too bad performance wise with fewer DIMMs at lower core count parts. 4 is probably good to start. The new IOD makes it better than the first gen for this.

7302P would be my pick BTW.
 

TXAG26

Active Member
Aug 2, 2016
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Make sure you get a version 2 Supermicro board. I’m looking into a similar setup, and with only 4 DIMM’s, I’m leaning towards DDR-3200 MHz speed ram. Seems about the same price as 2933 MHz.
 

alex_stief

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May 31, 2016
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Make sure you get a version 2 Supermicro board. I’m looking into a similar setup, and with only 4 DIMM’s, I’m leaning towards DDR-3200 MHz speed ram. Seems about the same price as 2933 MHz.
Beware: rev 2 boards usually don't support higher memory speeds. Your high frequency DIMMs will probably run, but at lower speeds.

How much performance will I loose when I go for 4DIMMs instead of 8?
Depends on how bandwidth-hungry your workloads are. There are workloads that can benefit from more than 4 memory channels, even with only 16 cores.
 

elag

Member
Dec 1, 2018
79
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Beware: rev 2 boards usually don't support higher memory speeds. Your high frequency DIMMs will probably run, but at lower speeds.


Depends on how bandwidth-hungry your workloads are. There are workloads that can benefit from more than 4 memory channels, even with only 16 cores.
According to Supermicro: H11SSL-i | Motherboards | Super Micro Computer, Inc. supports 2TB Registered ECC DDR4 3200MHz SDRAM in 8 DIMMs (Board revision 2.x required), so it should work...
I am not to worried about my work loads, they will normally be not too bad. I ordered today so when I get all stuff (will take up to 2 weeks) we will see where we end up
 

TXAG26

Active Member
Aug 2, 2016
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I can confirm my Rev. 2 H11SSL-NC with 7302P works great with 4x 32GB Supermicro (Samsung)
MEM-DR432L-SL02-ER32 (M393A4K40DB3-CWE) at both 3200MHz and 2933MHz. I even ran Memtest86+ for 48 hours with zero errors.
 

balnazzar

Active Member
Mar 6, 2019
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hi
How much performance will I loose when I go for 4DIMMs instead of 8? the new EPYC should loose less performance with 4 channels instead of 8 than the old ones, right?
The 7282 (I have it) has a four channel memory controller (so it does not matter if you install 4 or 8 modules), whereas the 7302P has 8 channels. If you live in america and don't mind the 155W tdp (I do), I urge you to buy the 7302P with the HPE deal. Below some benchmarks.
AMD-EPYC-4-Channel-Optimization-Performance.png
 
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sno.cn

Active Member
Sep 23, 2016
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AMD says 8 channels for 7282. I bought a pair for testing and returned them. But they didn't drive like quad channel CPUs.

Screen Shot 2020-02-04 at 9.05.51 PM.png
 

tsteine

Active Member
May 15, 2019
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AMD says 8 channels for 7282. I bought a pair for testing and returned them. But they didn't drive like quad channel CPUs.

View attachment 12946
Patrick has an article on why that is.
https://www.servethehome.com/amd-epyc-7002-rome-cpus-with-half-memory-bandwidth/

Essentially, the chiplet topology on the 7282 is such that there is no adjacent chiplet to the memory channel to the I/O die, so while it has 8 channels,it's limited to the bandwidth the IO die is able to feed to the available chiplets.
 

balnazzar

Active Member
Mar 6, 2019
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Patrick has an article on why that is.
https://www.servethehome.com/amd-epyc-7002-rome-cpus-with-half-memory-bandwidth/

Essentially, the chiplet topology on the 7282 is such that there is no adjacent chiplet to the memory channel to the I/O die, so while it has 8 channels,it's limited to the bandwidth the IO die is able to feed to the available chiplets.
Yes, the table I posted earlier was indeed taken from that (well-written) article. I think that AMD advertising the 120W Romes as 8-channel deserves to be harshly criticized. I bought the 7282, and I'm very satisfied with it, since for deep learning memory bandwidth is negligible, while processing power is not. Furthermore, I was aiming at achieving the best compute/power draw ratio. One further thing: since the 7282 essentially is a 3950X (single chiplet), it has 64Mb L3 cache, whilst other 16-core romes do have 128Mb (two 3950x chiplets with half cores deactivated but full cache).
No matter that, the capabilities of a 7282 don't deserve to be underestimated, since it has been shown that a 3950X actually stomps the 18-core intel Cascade Lake counterpart even with its dual channel memory. Last but not least, with `stress` and `stress-ng`, 32 threads, the cpu maintained a steady 3.2 GHz clock for 2 hours (its full steam frequency with 32T should just be 3.0 GHz). The total power drawn in such conditions was slightly more than 170W.
 
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sno.cn

Active Member
Sep 23, 2016
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I totally missed that article. I also missed the "Per socket memory bandwidth" figure in the screenshot I posted.
 
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