Intel SC5400RA User Guide - Page 44

Memory Sparing and Mirroring The chipset includes hardware that supports memory mirroring and memory on-line sparing. Both memory mirroring and memory on-line sparing provide a way to prevent data loss in case a FBDIMM fails. In determining your memory requirements, the need for memory sparing or memory mirroring must be considered. • The minimum FBDIMM population for memory mirroring is four DIMMs: DIMM_A1, DIMM_B1, DIMM_C1 and DIMM_D1. • The minimum FBDIMM population for memory sparing is eight DIMMs: DIMM_A1, DIMM_A2, DIMM_B1, DIMM_B2, DIMM_C1, DIMM_C2, DIMM_A1, and DIMM_A2. With memory mirroring the system maintains two copies of all data in the memory subsystem. If a FBDIMM fails, the data is not lost because the second copy of the data is available from the mirrored FBDIMM in the opposite channel. The system will not fail due to memory error unless both the primary and the mirrored copy of the data become corrupt at the same time. In a mirrored system, the maximum usable memory is one-half of the installed memory, with a minimum of four FBDIMMs installed. Since the data is duplicated across FBDIMMs, it means that up to one-half of the installed FBDIMMs are actively in use at any one time. The remaining FBDIMMs are used for mirroring. Memory mirroring and memory sparing are mutually exclusive. Only one can be active at a time. See the Intel® Server Board Technical Product Specification for additional information regarding the memory sub-system. 22 Intel® Server System SC5400RA User's Guide