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Memory 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.

Attention
Memory mirroring guidelines:

  • Mirroring can be configured across two channels.

  • Both channels must be populated in each iMC.

  • The total memory size of the primary and secondary channels must be the same.

  • Memory mirroring is supported when PMEMs are installed and set to 100% App Direct Mode.

  • Memory mirroring mode is limited to DDR4 memory modules only, PMEM memory mirroring is not supported in App Direct Mode.

ChannelsChannel 0Channel 1
SlotsSlot 1Slot 0Slot 1Slot 0
Identical DIMM installation required Y Y
Identical DIMM installation required for full channel mirroringYYYY
Note
When adding one or more DIMMs during a memory upgrade, you might need to remove some DIMMs that are already installed to new locations.

Mirror memory mode with one processor​

Table 1. Mirror mode with one processor
Total DIMMsProcessor 1Total DIMMs
12345678910111213141516
8*1357101214168*
16*1234567891011121314151616*
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.

Mirror memory mode with two processors​

Table 2. Mirror mode with two processors (processor 1)
Total DIMMsProcessor 1Total DIMMs
12345678910111213141516
16*13571012141616*
32*1234567891011121314151632*
Table 3. Mirror mode with two processors (processor 2)
Total DIMMsProcessor 2Total DIMMs
17181920212223242526272829303132
16*171921232628303216*
32*1718192021222324252627282930313232*
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.