Skip to main content

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.

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).

Figure 1. Processor and memory module layout: processor 1 and 2

Table 1. Processor and memory module layout: processor 1 and 2
1 DIMM 1-64 DIMM 7-18
2 DIMM 19-245 Processor 1
3 Processor 2 
Figure 2. Processor and memory module layout: processor 3 and 4

Table 2. Processor and memory module layout: processor 3 and 4
1 Processor 34 DIMM 43-48
2 DIMM 31-425 DIMM 25-30
3 Processor 4 
Table 3. Channel and slot information of DIMMs around a processor
Slot010101Processor101010
ChannelChannel 2Channel 1Channel 0Channel 0Channel 1Channel 2
DIMM number (Processor 1)123456789101112
DIMM number (Processor 2)131415161718192021222324
DIMM number (Processor 3)252627282930313233343536
DIMM number (Processor 4)373839404142434445464748