X11-DPHT Memory Recommendations

[wpj]

With Intel QL1F and Supermicro X11DPH-T what would be the fastest memory configuration if 12/8 DIMM's are populated for total of 192/128 GB each 16 GB modules;

1. Single Ranked X4
2. Dual Ranked X4

Single Rank seems faster but I am reading interleaving on channel then interleaving on module happens and it is beneficial to have interleaving on modules means at least dual rank.

Memory Deep Dive: Optimizing for Performance - frankdenneman.nl

Also will CL19 (2666) hurt over CL17 (2400) or the difference is too miniscule?

 

[alex_stief]

One dual-rank DIMM per memory channel with the maximum supported frequency is usually the fastest possible configuration.
Don't worry about latency, the CL value has a unit of cycles, not time. So the actual access times are about the same, but faster memory achieves higher bandwidth.
And if you are really concerned with memory performance, use 6 DIMMs per CPU for Skylake-SP, not 4.

 

[ErikAnd]

Lenovo has publiced reports about various memory configuration. Even though that is not SuperMicro, the memory controller is the same. Se https://lenovopress.com/lp0697.pdf for a comparison between single and dual rank memory. The conclusion is on page 11. (use dual rank)
Lenovo has also looked on the impact of using different number of DIMMs per cpu, see https://lenovopress.com/lp0742.pdf
Conclusion: always use 6 or 12 DIMMs per CPU. The motherboard you are looking at does not have room for 12 DIMMS per CPU, so use 6. If the boards 16 positions for DIMMS are all used the memory bandwidth performance will be bad, according to the report.

 

[wpj]

Thank You All.. I am aware that to make it perfectly balanced and utilize full bandwidth I need to put in 6 slots per CPU. Here is the catch; I have access to currently either;

1. Crucial 16GB DDR4-2666 RDIMM | CT16G4RFS4266 | Crucial.com Single Rank X4 2666 Mhz
2. Hynix Dual Rank X8 2400 Mhz

I do not have access to a Dual rank AND x4 chip. So which one should I choose?

 

[ErikAnd]

If the processor in question just supports up to 2400 MHz, then chose option 2 .
For processors supporting 2666 MHz, I think, the two memory options will perform nearly the same.
Based on https://lenovopress.com/lp0697.pdf the bandwidth scales with frequency. When two dual rank DIMMs are used for each channel, the performance is set to 100 %. With just one dual rank DIMM per channel, the performance is 96 %, and multiplied with 2400/2666 it becomes 86,4 %.
According to the report, one single rank DIMM per channel performs at 87 %. In other words, the two options will perform nearly the same, and at a about 11 % lower performance than the optimal solution for your motherboard, obtained with one dual rand DIMM per channel at 2666 MHz.
The Lenovo report uses 2Rx8 and 1Rx4 DIMMs which are similar to your memory options except for the frequency.