That is correct, you can go with 4 or 8. For maximum performance you would want to populate across all 4, but as you saw it wasn't stating it was an unsupported configuration at 6, but it isn't recommended based on performance.

Umirza85,

That is correct, as seen on page 45-46 in the manual found here , there isn't a 6 dimm supported configuration. Also you were almost correct, it is 4 dimms per processor, or 1 dimm per channel, across the 4 channels. So I would agree with you that you will need to add a couple dimms to maximize performance. 

Let me know if this helps.

Hi Chris, I'm really struggling here as my expected times are double what they should be so thanks for the response.

I just dont understand why 2 extra dimms for 6 total (in slots A3/B3) could cause the everything to slow down like that...I thought that as they're installed in pairs that and fill the channel on both processors that it shouldnt be an issue. But are we saying here that with two processors the dimms always need to be installed across all 4 channels for both processors?

So i can add 2 dimms, but could i also for now perhaps remove 2 dimms (for 4 total installed/2 per processor) to increase my performance?

As an FYI the 6 memory modules are all 16GB (1x16GB) Dual Rank x4 PC3-14900R (DDR3-1866) Registered CAS-13 Memory Kit

Thanks very much.

I wish I knew this previously, I've removed 2 of the DIMMS and have 4 and performance has picked up to where I think it should be...its definitely about 30-35% faster then before.

Thats quite a drastic dip in performance for adding the 5th,6th DIMM, IDRAC and the system were all reporting the memory as expected at 1866 without any issues, is there any way to tell that the performance from the installed ram is not optimal? Would a benchmark in something like AIDA 64 show this performance drop?

Thanks again, i suppose I'll run some more tests at 4 DIMMS, and then order 2 more (for 8 total) if the performance numbers stay where they should.

I wish I had asked here before, i've spent an uncountable number of hours troubleshooting everything else but the memory as nothing was showing an error (or unsupported).

Thanks Chris.