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Memory mirroring mode installation order

Memory-mirroring mode provides full memory redundancy while reducing the total node 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 node.

Memory mirroring guidelines:

  • Memory mirroring reduces the maximum available memory by half of the installed memory. For example, if the node has 64 GB of installed memory, only 32 GB of addressable memory is available when memory mirroring is enabled.

  • Each DIMM must be identical in size and architecture.

  • DIMMs on each memory channel must be of equal density.

  • If two memory channels have DIMMs, mirroring occurs across two DIMMs (channels 0/1 will both contain the primary/secondary memory caches).

  • If three memory channels have DIMMs, mirroring occurs across all three DIMMs (channels 0/1, channels 1/2, and channels 2/0 will all contain primary/secondary memory caches).

  • Partial Memory Mirroring is a sub-function of memory mirroring. It requires following the memory installation order of memory mirroring mode.

With one processor​

The following table shows the DIMM population sequence for memory mirroring when one processor is installed.

Table 1. Memory Mirroring with one processor
Total DIMMsProcessor 1
87654321
8†

8

7

6

5

4

3

2

1

Note

† Sub NUMA Clustering (SNC2) feature can only be enabled when DIMMs are populated in this specified sequence. The SNC2 feature can be enabled via UEFI.

With two processors​

The following table shows the DIMM population sequence for memory mirroring mode when two processors are installed.

Table 2. Memory mirroring with two processors
Total DIMMsProcessor 1
87654321
8†

8

7

6

5

4

3

2

1

Total DIMMsProcessor 2
910111213141516
16†

9

10

11

12

13

14

15

16

Note

† Sub NUMA Clustering (SNC2) feature can only be enabled when DIMMs are populated in this specified sequence. The SNC2 feature can be enabled via UEFI.