Memory Utilization issue in Dell Server R810.

Dear Concern,

one our valued customer facing issue in R810 server memory utilization from memory redundancy option.

I have installed physical memory 128GB (4GB module) but showing 112GB from OS.

Our Troubleshoot step:

1. Try to change memory redundancy option Spare to Disable.
2. Flash BIOS 2.7.4 to 2.9
3. Reset all physical memory but issue is not resolve.

Note: Memory Redundancy Option set always Disable and not changeable like Spare, optimization or mirror.

Please suggest me how can I solve this issue.