When you mix them, does the server turn on and get past the "Configuring Memory" message? If the system is able to work around any misconfiguration it would then prompt with details (such as available memory may be reduced, cannot put X in X slots etc). Make sure your BIOS is up to date (6.4.0) for the most up to date memory support. If you have to update the BIOS update the Lifecycle controller and iDRAC as well if needed. The standard Dell support answer is that these three items must be on current versions. If it works with the 2x8Gb and the 4x2Gb separately, check you are not trying to mix Registered/ECC memory and Unregistered memory together. If the server is not booting up properly this is likely. Google search the part numbers to check. Check if the BIOS memory mode is Optimizer Put the two 8Gb in A1/B1 Put four 2Gb in A2/A3 B2/B3 Let us know how it goes! Note: This answer is based on my own general experience of the R710 and I am not a member of Dell support, just an end user. Better answers from other people may follow.
Hi, For r710 server that I have i've purchased a memory kit: 2 piece of 8 GB. The current Ram config is 4 modules of 2 GB each.  the server is dual CPU, so the memory are in A1 A2 and B1 B2. could you please help how to arrange to dimms so it can work with all of them.  Separately it work but not together, and i've tried different configurations. Thanks
Dell R710 Memory upgrade