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Mirroring mode

Memory-mirroring mode provides full memory redundancy while reducing the total system memory capacity in half. Memory channels are grouped in pairs with each channel receiving the same data. If a failure occurs, the memory controller switches from the DIMMs on the primary channel to the DIMMs on the backup channel. The DIMM installation order for memory mirroring varies based on the number of processors and DIMMs installed in the server.

In mirroring mode, each memory module in a pair must be identical in size and architecture. The channels are grouped in pairs with each channel receiving the same data. One channel is used as a backup of the other, which provides redundancy.

Follow the rules below when installing memory modules in mirroring mode:

  • All memory modules to be installed must be of the same type with the same capacity, frequency, voltage, and ranks.

  • Mirroring can be configured across channels, and the total DDR4 memory size of the primary and secondary channels must be the same.

  • Partial Memory Mirroring is a sub-function of memory mirroring. It requires to follow the memory population for memory mirroring.

The following table shows the memory module population sequence for mirroring mode when only one processor (CPU 1) is installed.

Table 1. Mirroring mode with one processor (CPU 1)
ConfigurationDIMM slots
12345678910111213141516
8 DIMMs135710121416
16 DIMMs12345678910111213141516
Note
DIMM configurations listed in the table support the Sub NUMA Clustering (SNC) feature, which can be enabled via UEFI. SNC is not supported if DIMM population does not follow the sequence indicated by the table above.

The following table shows the memory module population sequence for mirroring mode when two processors (CPU 1 and CPU 2) are installed.

Table 2. Mirroring mode with two processors (CPU 1 and CPU 2)
ConfigurationDIMM slots
12345678910111213141516
16 DIMMs135710121416
32 DIMMs12345678910111213141516
ConfigurationDIMM slots
17181920212223242526272829303132
16 DIMMs1719212326283032
32 DIMMs17181920212223242526272829303132
Note
DIMM configurations listed in the table support the Sub NUMA Clustering (SNC) feature, which can be enabled via UEFI. SNC is not supported if DIMM population does not follow the sequence indicated by the table above.