Memory mirroring mode installation order
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.
Memory mirroring guidelines:
• Memory mirroring reduces the maximum available memory by half of the installed memory. For example, if
the server 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).
With two processors
The following table shows the DIMM population sequence for memory mirroring when two processors are
installed.
Table 28. Memory Mirroring with two processors
Total Processor 1 Processor 2 Total
DIMMs 1 2 3 4
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 DIMMs
8* 3 5 8 10 15 17 20 22 8
12* 1 3 5 8 10 12 13 15 17 20 22 24 12
24* 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 24
Note: DIMM configurations with an asterisk (*) 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.
With four processors
The following table shows the DIMM population sequence for memory mirroring mode when four processors
are installed.
Table 29. Memory mirroring with four processors
Total Processor 1 Processor 2 Total
DIMMs 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 DIMMs
16* 3 5 8 10 15 17 20 22 16
24* 1 3 5 8 10 12 13 15 17 20 22 24 24
48* 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 48
Total Processor 3 Processor 4 Total
DIMMs 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 DIMMs
16* 27 29 32 34 39 41 44 46 16
156 ThinkSystem SR860 V2Setup Guide
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