Rank sparing

Sparing enables a failing rank to be replaced by ranks installed in an unoccupied space. An unused spare rank on the channel can be used to copy the contents of a failing rank on that channel.

When you use the memory mirroring feature, consider the following information:

In rank sparing mode, one rank of a DIMM in each populated channel is reserved as spare memory. The spare rank is not available as active memory. When the active rank memory fails, its content is copied to the spare rank memory which becomes active. The spare rank must have identical or larger memory capacity than all the other ranks on the same channel.
DIMMs must be installed in sets of three. The DIMMs in each set must be the same size and type.
The following table lists the DIMM installation sequence for rank sparing mode when one or two microprocessors is installed in the server:

The following table shows the installation sequence for installing DIMMs for each microprocessor in memory online-spare mode:

Table 1. DIMM population sequence (rank sparing mode).
Two column table for documenting DIMM connector population sequence for microprocessors 1 and 2.
Number of installed microprocessors	DIMM connector population sequence
1	8, 7
	1, 2
	6, 5
	3, 4
2	8, 7, 16, 15
	6, 5
	14, 13
	1,2
	9, 10
	3, 4
	11, 12

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