Dual Channel 4 DIMMs 2x8G + 2x16G, is this a good idea?

[SaberLo]

Hi everyone, I am a master student doing computational chemistry. Our lab recently built a workstation with the follwoing specs:

 

CPU: 3950x

Mobo: ASUS Pro WS X570-ACE

RAM: G.SKILL F4-3600C16D-16GVKC (2x8G)

Boot NVMe: Sabrent 1TB Rocket NVMe 4.0

GPU: ASUS 2080ti Turbo

(Also various HDD for data storage)

OS: Ubuntu 19.10

 

We are currently running a lot (millions) of small jobs and trying to take advantage of the large number of cores/threads on the 3950x, but we found that if we run more than 5 jobs at the same time, we will run out of RAM. Although we have swap spaces on the PCIe 4.0 drive, we still want to process our data as fast as possible. We plan to put more RAM on the machine, but we don't want to limit ourselves to 32GB by simply adding another 2x8G (since that will still not allow us to fully utilize all 16c/32t), therefore we are wondering if adding 2x16G would work well. If so, is there a specific kit that we should get?

 

TLDR: We have 16GB of RAM now, we want to add another 32GB to the machine, is this a good ideal?

 

Thanks in advance!

[porina]

Capacity wise should be ok. I don't know if you'll be able to maintain 3600 speeds though so there may be impact to that. 

[SaberLo]

1 minute ago, porina said:

Capacity wise should be ok. I don't know if you'll be able to maintain 3600 speeds though so there may be impact to that. 

Yeah, we are concerned about that too. If we end up doing it, we are thinking at least getting RAMs with same latency and speed. Do you have any experience with that?

[SenKa]

This is one of those very not agreed upon topics in the PC space. While it is FAR from optimal, it should be stable so long as you run at the frequency and timings of the slower set.

 

Why not just do 4x 16GB Sticks and resell the 8GB ones? Too much cost?

[TomvanWijnen]

I've ran a DDR3 system with 2x4GB + 1x8GB for years without issues, and had many DDR2 systems with much weirder configurations. This is of course just anecdotal evidence, but most people have reported being able to run different kinds of RAM without any issues. In the unlikely case that issues would occur, you should be able to just sell the 2x8 GB sticks.

[SaberLo]

1 hour ago, SenKa said:

This is one of those very not agreed upon topics in the PC space. While it is FAR from optimal, it should be stable so long as you run at the frequency and timings of the slower set.

 

Why not just do 4x 16GB Sticks and resell the 8GB ones? Too much cost?

We would like to do that too, but adding another 2 x 16GB is a "simpler" solution, since we don't have to deal with reselling things or what not. Cost is one of the reasons too, because we have to pay from our own funding; the school will not pay for this...

[SaberLo]

55 minutes ago, TomvanWijnen said:

I've ran a DDR3 system with 2x4GB + 1x8GB for years without issues, and had many DDR2 systems with much weirder configurations. This is of course just anecdotal evidence, but most people have reported being able to run different kinds of RAM without any issues. In the unlikely case that issues would occur, you should be able to just sell the 2x8 GB sticks.

Thanks for the info and suggestion! We might just try and see what happen.

[porina]

1 hour ago, SaberLo said:

Yeah, we are concerned about that too. If we end up doing it, we are thinking at least getting RAMs with same latency and speed. Do you have any experience with that?

I've tried 4x16 3200 in my X370 - 3700X system and that was ok. My B450 - 3600 system didn't even want to run 2 sticks (all it can take) at 3200. So there will be some unknowns due to mobo. My concern remains that 3600 might be challenging with that much ram, so even if you bought 2x16 3600 kit, you might have to run slower than that for stability. As you go towards 3200 your chances should increase but even then I can't say with 100% certainty it'll work.

 

I have run mismatched ram in other systems without problems. As expected, you end up running the slowest of whatever you mix. My laptop for example has two 8GB sticks, one 2133 2R (had spare), the other 2400 1R (built in). I loss a little speed but still gain from dual channel in this case.

 

I've probably mixed and match elsewhere before, more in DDR3 and even DDR2 era since ram is more affordable in DDR4 era. It is never 100% but worked more often than not. I wouldn't be worried about a 2x16+2x8 configuration, as long as you accept there will be some risk it wont run at higher speeds. The important thing will be to ensure the ram is still matched in channels. Counting 1 from the CPU side, I'd put the 8GB modules in 1+3, and 16GB in 2+4. Check if your mobo manual might offer advice in that respect.

[SaberLo]

13 minutes ago, porina said:

I've tried 4x16 3200 in my X370 - 3700X system and that was ok. My B450 - 3600 system didn't even want to run 2 sticks (all it can take) at 3200. So there will be some unknowns due to mobo. My concern remains that 3600 might be challenging with that much ram, so even if you bought 2x16 3600 kit, you might have to run slower than that for stability. As you go towards 3200 your chances should increase but even then I can't say with 100% certainty it'll work.

 

I have run mismatched ram in other systems without problems. As expected, you end up running the slowest of whatever you mix. My laptop for example has two 8GB sticks, one 2133 2R (had spare), the other 2400 1R (built in). I loss a little speed but still gain from dual channel in this case.

 

I've probably mixed and match elsewhere before, more in DDR3 and even DDR2 era since ram is more affordable in DDR4 era. It is never 100% but worked more often than not. I wouldn't be worried about a 2x16+2x8 configuration, as long as you accept there will be some risk it wont run at higher speeds. The important thing will be to ensure the ram is still matched in channels. Counting 1 from the CPU side, I'd put the 8GB modules in 1+3, and 16GB in 2+4. Check if your mobo manual might offer advice in that respect.

Thank you so much! This is helpful, we will try that configuration out. The manual definitely include info about the channels (we've read through that before).

[SenKa]

3 hours ago, SaberLo said:

We would like to do that too, but adding another 2 x 16GB is a "simpler" solution, since we don't have to deal with reselling things or what not. Cost is one of the reasons too, because we have to pay from our own funding; the school will not pay for this...

Fair enough. You SHOULD be fine. @porina basically nailed what you should do. 

[SaberLo]

8 minutes ago, SenKa said:

Fair enough. You SHOULD be fine. @porina basically nailed what you should do. 

Thank you! I understand it's not the most elegant way to do it, but we will try and see how it works out.