Memory mirroring in lockstep mode

Use this information for notes and details about using the memory mirroring feature in lockstep memory mode.

Memory-mirroring replicates and stores data on DIMMs across all four memory channels for the compute book and DDR3 or DDR4 channels simultaneously. If a failure occurs, the memory controller switches from the DIMMs on the primary channels to the DIMMs on the backup channels.

To enable memory mirroring through the Setup utility, select System Settings → Memory → Memory Mode. For more information, see Using the Setup utility. For more information and notes about installing DIMMs, see Installing a memory module and Lockstep memory mode.

Consider the following information when using the memory mirroring feature in lockstep memory mode:

• The compute book memory channel 0 mirrors memory channel 1, and memory channel 2 mirrors memory channel 3. This mirroring provides redundancy in memory but reduces the total memory capacity in half.
• DIMMs must be installed across the memory channels for each compute book when using the memory mirroring feature in lockstep mode.
• The DIMM population must be identical (size, organization, etc.) for memory channel 0 and memory channel 1, and identical for memory channel 2 and memory channel 3.
• 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.
• The following table lists the DIMM installation sequence for memory mirroring in lockstep memory mode:

  Table 1. DIMM population sequence when memory-mirroring is enabled or disabled in lockstep mode.

  Three-column table with headers that lists the population sequence with memory-mirroring enabled or disabled in lockstep memory mode

  DIMM installation order	Lockstep mode with memory mirroring disabled	Lockstep mode with memory mirroring enabled
  1	DIMM connectors 9 and 15	DIMM connectors 1 and 9, and DIMM connectors 15 and 19
  2	DIMM connectors 6 and 24	DIMM connectors 6 and 10, and DIMM connectors 16 and 24
  3	DIMM connectors 1 and 19	DIMM connectors 2 and 8, and DIMM connectors 14 and 20
  4	DIMM connectors 10 and 16	DIMM connectors 5 and 11, and DIMM connectors 17 and 23
  5	DIMM connectors 8 and 14	DIMM connectors 3 and 7, and DIMM connectors 13 and 21
  6	DIMM connectors 5 and 23	DIMM connectors 4 and 12, and DIMM connectors 18 and 22
  7	DIMM connectors 2 and 20
  8	DIMM connectors 11 and 17
  9	DIMM connectors 7 and 13
  10	DIMM connectors 4 and 22
  11	DIMM connectors 3 and 21
  12	DIMM connectors 12 and 18