[jarjarbinks]

I checked them out, but they seem to be opened and unboxed cpus. Is it safe to buy them? They don't seem to have any brand new boxed ones. And how safe is it to buy from chinese sellers? See this: https://www.ebay.ca/itm/175825538137...Bk9SR8KTqbL8Yg

[MangoNrFive]

I have read a bit more about building workstations for CFD and I read, that dual-rank RAM is preferable for CFD with a speedup of 10%-15% versus single-rank.

The RAM that I selected until now is single-rank:
1956€ 24x Kingston Server Premier RDIMM 16GB, DDR5-4800, CL40-39-39, 1x8, reg on-die ECC

On the QVL of the MB there are modules available with dual-rank as well, though only for the more expensive 32GB-modules, like this one:
3336€ 24x Kingston Server Premier RDIMM 32GB, DDR5-4800, CL40-39-39, 2x8, reg on-die ECC

The increase in the amount of available memory is not a factor for us, as the 384GB from the 16GB-modules is more than enough. But if we indeed would get a 10%-15% performance-increase that could be worth the price.

Another question, is the number of banks a relevant factor for CFD in this configuration, or should I look only at the ranks? All the modules on the QVL have either 4 or 8 banks with both combinations of ranks (e.g. 1x4, 1x8, 2x4, 2x8 is available).

[flotus1]

According to benchmarks done by AMD for the release of Epyc Genoa, one or two ranks per channel perform nearly identical with DDR5.
The performance difference was much larger for DDR4 and older. In my opinion, it is not worth spending extra just to get two ranks per channel with DDR5.
Number of banks: as long as it is not x16, even I don't care. Both x4 and x8 are fine.
https://www.servethehome.com/wp-cont...-Bandwidth.jpg
See also AMD Epyc 9004 "Genoa" buyers guide for CFD