Set the Select Memory RAS Configuration to Mirroring.
Return to the Memory Configuration menu option.
Make sure Current Configuration indicates Memory
Mirroring Mode. If the option indicates Current Memory
Configuration, you may need to install more memory to
meet the requirements of the selected configuration.
Make sure that Memory Mirroring Possible indicates Yes.
Press F10 to save changes and exit.
Press Y to confirm. The server reboots to activate the changes.
Appendix B: Memory configuration