Hi Mpolo, With the PowerEdge R710, there's numerous memory configurations that will work correctly but what you appear to be trying with your existing servers will not work. A little bit of background on this: each processor has an embedded memory controller and in this case, each memory controller controls 9 available memory slots - 3 channels of 3 memory slots each. There are also several memory modes. Without going into too much detail, you have Advanced ECC (Lockstep) mode, Memory Mirroring mode, Memory Sparing and Memory Optimized (Independent Channel) mode. You've got 8 x 2GB DDR3 memory sticks, either UDIMMs (unbuffered), RDIMMs (registered) or LV RDIMMs (low voltage registered). With this set-up, your system will be in either Advanced ECC (Lockstep) mode or Memory Mirroring mode. In these modes, your system can only use 2 out of the 3 channels per processor so in total, there are 12 available memory slots. For your current configuration, each channel has 2 x 2GB DDR3 memory sticks installed and there is one slot free per memory channel. Your proposal to install 4 x 4GB DDR3 memory sticks will not work because the server does not support memory mixing for either Advanced ECC (Lockstep) mode or memory mirroring mode.  You could install 6 x 2GB DDR3 and 6 x 4GB DDR3 in either Memory Optimized mode or Memory Sparing mode. This would give 36GB of available memory. This is assuming that your 2GB DDR3 memory sticks are single-ranked or dual-ranked and that your 4GB DDR3 memory is dual-ranked. Regarding purchasing a new server, there is a configuration available with 4 x 8GB DDR3 RAM. This is using Advanced ECC (Lockstep) mode but this particular configuration only allows use of one processor.
I have a couple of R710 servers with 8 x 2GB DD3 RAM (out of 18 slots). I am looking to add another 16 GB to the server but the Dell tech support person is warning me that if I go with 4 x 4GB RAM sticks there will be compatibility issues. What are these compatibility issues he is talking about? Also we are looking to purchase a new R710 server with 32 GB and we wanted to have 4 x 8GB RAM but again support person says 8GB sticks support only 3+ processors. I don't understand the relation between RAM and CPU. Dell page says it supports only processors with 2/4/8/16GB sized RAM modules.  I would appreciate if someone can clear this up. Thanks.
RAM Upgrades