With today's memory prices, a frequent question at Phoronix and throughout many organizations is about reducing cost by not necessarily populating all memory channels. Especially with modern servers going up to 12 memory channels per socket or even 16 memory channels with upcoming EPYC Venice, you may be curious about the performance impact of populating less memory channels to see if the trade-off is worthwhile given today's DDR5 RDIMM pricing. In this article are benchmarks from a Dell PowerEdge server looking at a dual AMD EPYC 9655 2P configuration when testing between four and the full twenty-four DDR5-6400 RDIMM configuration and the resulting performance impact in more than 250 benchmarks.

Dell supplied gratis remote access to a Dell PowerEdge R7725 2U server platform for conducting these tests with a dual EPYC 9655 2P configuration and then swapping out to different supported memory populations of 4, 8, 10, 12, 16, 20, and 24 RDIMMs between the two EPYC Turin processors.

The memory used were Hynix HMCG94AHBRA480N 64GB DDR5-6400 RDIMM memory modules. With the Dell PowerEdge R7725 product page currently lists the 64GB RDIMM modules at $8,260.92 USD each. Thus with a full load-out of 24 x DDR5-6400 RDIMMs with the Dell list prices comes in at $198,240 USD... Or around $222k USD at today's prices for the Dell PowerEdge R7725 server with the AMD EPYC 9655 96-core processors and the 24 memory modules. Given the memory pricing in the industry, many will want to run at less than a full 24 memory module configuration at least until prices subside.

These benchmarks carried out on Ubuntu 26.04 LTS with the Linux 7.0 kernel are designed to provide some reference numbers across a wide range of workloads for seeing the resulting performance impact across 4 / 8 / 10 / 12 / 16 / 20 / 24 memory channels without making any other software/hardware changes between runs. Thanks to Dell for providing the free remote access for making these benchmarks possible.