Epyc 7002 build - 4 vs. 8 RAM sticks

[FaSti]

I’m putting together an AMD EPYC Rome based machine. The board I’m using ist ASRock’s ROMED8-2T. I’m planing to run TrueNAS Scale (Debian based).
Does it matter weather I use 4 RAM sticks (32 GB, ECC, DDR4, dual rank, CL22) or 8 RAM sticks (16 GB, ECC, DDR4, single rank, CL22)?

[Exard3k]

@FaSti

Does it matter weather I use 4 RAM sticks (32 GB, ECC, DDR4, dual rank, CL22) or 8 RAM sticks (16 GB, ECC, DDR4, single rank, CL22)?

Memory Bandwidth will of course differ. 4 sticks = 4 channels, 8 sticks = 8 channels. Other than that I recommend checking the board manual to check if the board supports a 4 stick configuration. But 8 stick configuration is pretty much the standard for EPYC.

[madal38089]

I think it doesn’t matter

[Ruklaw]

If you are using one of the four-channel optimized cpus then it definitely won’t matter either way:

AMD EPYC 7002 Rome CPUs with Half Memory Bandwidth

Otherwise it’s likely to matter only on benchmarks, real world stuff is likely to do fine with four memory channels.

We’re running our Epyc servers at work with four sticks, I figure it means if we decide to upgrade ram capacity we get the added benefit of more bandwidth too…

[khoidang]

Haven’t used ROMED8-2T, but I ran my 7402 on 4 channel for a while (not even the correct 4 channels) and it worked fine. You probably won’t run into any issues

[FaSti]

This article was definitly helpful. I had planed to use the 8282 but did not konw that there is a difference in Memory bandwith. Now i understand why it is so much cheaper than the 7302 even though it comes with 16 cores as well. Now I changed my plans and will go with the 7302. 4 32 GB DIMMs will do to get started and i will uprade later

[jtredux]

All of the channels have their own memory controller - the more channels you populate, the more bandwidth the whole CPU cluster has, but individual cores have their own limits.

You can populate just one channel if you like, but it won’t be optimal to say the least. Personally I stuff as many channels as I can afford with the biggest DIMMs I can afford and upgrade bandwidth/capacity later if I need it and can afford it, so I’m running 4x 32GB at the moment and may end up with 8x32GB or 4x32 + 4x64GB at some point.