X11DPG-QT Memory Config & Performance

[kromberg]

OK, I got one of these coming in for a server upgrade. It has a total of 16 DIMM slots that I was populating with the 32GB sticks. After looking at the manual, I noticed in the memory config section that supports and recommends up to 12 DIMMs as using 14 or 16 DIMMs results in the unbalanced config and performance drop. Really????!?! Why would you put 16 slots, but only recommend 12? How bad is the performance drop if you populate with 16 DIMMs?

 

[BlueFox]

LGA 3647 has 6 channel memory, so, you want multiples of 12 (with 2 CPUs) for optimal performance. This isn't a Supemicro thing. Normally the remaining slots are used for Optane DIMMs. Some setups need more memory over higher performance as well.

 

[RolloZ170]

the memory controller is a hexachannel.
the add.black slots are just secondary slots of channel A and D. use them for DC pers.memory(AD mode) or if you need the more memory.
the perf. loss depends on your application. the synthetic benchmarks can't tell you.

 

[RolloZ170]

How bad is the performance drop if you populate with 16 DIMMs?

should drop from 6 channel to 2 channel. its hard to measure.
i have tested 6 vs 5 channel (unbalanced) in AIDA64 and got 60 vs 50 points in relative.

 

[kromberg]

Thanks for the replies everyone, that makes sense now.

LGA 3647 has 6 channel memory, so, you want multiples of 12 (with 2 CPUs) for optimal performance. This isn't a Supemicro thing. Normally the remaining slots are used for Optane DIMMs. Some setups need more memory over higher performance as well.

Hmmm..... I didnt think of that as I dont have much experience with Optnes. At least from my quick reading here, If you add some in the last/outer four slots and set those slot to be "App Direct", then they should should up as a SSD to the os? I assume if you mix the speed of the Optanes and DIMMs, which ever has the slower speed will be what everything runs as? Or do they all need to have the same speed?

 

[RolloZ170]

Hmmm..... I didnt think of that as I dont have much experience with Optnes

you must not use optane.

I assume if you mix the speed of the Optanes and DIMMs, which ever has the slower speed will be what everything runs as?

correct. in AD mode the two black slots are used separated from the other 6 slots. this requires BIOS/UEFI support.

 

[kromberg]

you must not use optane.

So just to confirm using Optane DIMMs with this setup is like poking a T-Rex with a short stick? Not a good idea.

 

[BlueFox]

It's a more complex setup. You need a Cascade Lake generation CPU to support it anyway (Skylake won't work).

 

[kromberg]

It's a more complex setup. You need a Cascade Lake generation CPU to support it anyway (Skylake won't work).

Well that popped by idea balloon