Lenovo System x3850 X6 Installation And Service Manual page 70

• 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.
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System x3850 X6 and x3950 X6 Installation and Service Guide