Memory rank sparing in lockstep mode

The server supports memory rank sparing. Memory rank sparing reserves memory capacity for failover in the event of a DIMM failure, and the reserved capacity is subtracted from the total available memory. Memory sparing provides less redundancy than memory mirroring does. If a predetermined threshold of correctable errors is reached, the contents of the failing DIMM are copied to the spare memory, and the failing DIMM or rank is disabled.

To enable memory sparing 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.

The DIMM installation order for memory rank sparing follows the independent mode (performance) or lockstep mode (RAS) installation order based on the mode of operation selected. For more information, see Independent memory mode, and Lockstep memory mode.

Consider the following when using the memory rank sparing feature in independent memory mode:

• Memory rank sparing is not supported if memory mirroring is enabled.
• The spare rank must have identical or larger memory capacity than all the other ranks on the same DDR3 or DDR4 channel.
• When single-rank DIMMs (that is, 4 GB and 8 GB) are used, a minimum of two rank DIMMs must be installed per memory channel to support memory sparing.
• When multi-rank DIMMs (that is, 16 GB, 32 GB, and 64 GB) are used, one multi-rank DIMM can be installed per memory channel to support memory sparing.
• The total memory available in the system is reduced by the amount of memory allocated for the spare ranks.