I have a Dell PowerEdge R720xd and I am trying to increase the memory. The Bios is 2.7.0 and the CPUs are dual E5-2690s.

The system has been running fairly well with eight of these fitted MICRON MT18JSF1G72PZ-1G6D1FE 8GB 1RX4 PC3-12800 DDR3 1600MHZ SDRAM - SINGLE RANK ECC REGISTERED CL11 240-PIN MEMORY.

I bought eight of these, SAMSUNG M393B2G70BH0-CK0 16GB 12RX4 PC3-12800 1600MHZ SDRAM - DUAL RANK ECC REGISTERED CL11 1.5V DDR3 240-PIN RDIMM and seem to be limited in what I can achieve so far.

If I put only the 16Gb modules in, then it never gets past the configuring memory message. If I put one in 16Gb module in A1 and one in B1 and no other memory in the system, I get the same problem. If I put an 8Gb in A1/B1 and 16Gb in A2/B2, then all is well, then I can add 16Gb sticks to A3/B3 and A4/B4 and I get to 112Gb and all is well (that’s as far as I have got as each step takes so much time).

If I put 16Gb in A1/B1 and 8Gb in A2/B2, I get past configuring memory, but then get a memory failure in Dimm A1 message ("MEMBIST MemoryTest failure DIMM A1"). If I swap the sticks between A and B, the message is still about an error in A1 (suggests not the individual sticks?).

In system setup I have resorted to turning off system memory testing and node interleaving is disabled. Ideally I think I want the 16Gb sticks in A1-A4 and the 8Gb sticks in A5-A8, with the same configuration in the B slots and node interleaving back on?

Tonight I will continue adding sticks in pairs and see if it runs with all 16 sticks installed (I have one 750W power supply, the system normally draws around 200W, hits 500W at peak.

Is there something else I am missing, some setting I should adjust? I have left it on the configuring memory for 2-3 hours with no change (it normally takes 5-10 seconds), does it need longer?