Will server just not recognize memory sticks or downgrade to max supported speed of 2400 MT/s? Memory sticks I had in mind are from my desktop that can run at 2800 MT/s DDR4.
I am waiting for server to arrive to test myself but I’d figure someone might know the answer before I find out for myself.
Yes and no, an R630 is only able to run RDIMM and LRDIMM at 1866, 2133, and 2400 MT/s, due to the generation of processor it supports. Anything higher than 2400 MT/s will be just be stepped down to the next speed. You are better off buying the maximum supported configuration rather than buying something out of spec.
RAM speed support depends on the CPU. From the top of my head, the R630 doesn’t go further than 2400MT/s, neither do more than threequarter of the CPUs that can work in that machine.
You can put in DDR4-4000 if you want, but the machine will downclock it to 2400, because it can’t go much faster than that.
And why wouldn’t you want to go with ECC REG? It’s cheap, there is plenty of it and you can stuff in 3TB of it. Non-ECC can only go to 64GB I believe.