Power Edge R710: Memory arrangement

Hello,

I have 4 memory DIMMs of 40 Gb total size I want to install on my R710. the DIMMs are distributed as follow:

4x 2Gb

4x 8Gb

I tried sevral arrangements of DIMMs:

8-2-0-8-2-0-0-0-0***0-0-0-0-2-8-0-2-8

8-8-0-2-2-0-0-0-0***0-0-0-0-2-2-0-8-8

2-2-0-8-0-0-8-0-0***0-0-8-0-0-8-0-2-2

but at the end, I only get 32 Gb of available memory.

How can I get 40Gb of total available memory.

Thanks.