7420 active/active cluster usable memory considerations

Hi,
I'm trying to understand why even if 512G RAM is installed on each cluster head, active memory is only 256G on each controller.



When I look at DIMM details on each head I have this kind of information from CLI:

memory-052   P2/MR0         ok        Oracle                  FRUID,PI,ASSY_MEM_RSR_M2,CLLS             0328MSL-1223TA1L7X
memory-053   P2/MR1         ok        Oracle                  FRUID,PI,ASSY_MEM_RSR_M2,CLLS             0328MSL-1223TA1L6G
memory-054   P3/MR0 DIMM 0  ok        SAMSUNG                 8GB DDR3 SDRAM 666                        85D0ED98
memory-055   P3/MR0 DIMM 1  ok        unknown                 unknown                                   unknown
memory-056   P3/MR0 DIMM 2  ok        SAMSUNG                 8GB DDR3 SDRAM 666                        85D0ED48