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Memory modules of different capacities can be mixed provided other memory population rules are followed.
For example, 4 GB and 8 GB memory modules can be mixed.
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In a dual-processor configuration, the memory configuration for each processor must be identical.
For example, if you populate socket A1 for processor 1, then populate socket B1 for processor 2, and so on.
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Mixing of more than two memory module capacities in a system is not supported.
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Unbalanced memory configurations will result in a performance loss so always populate memory channels identically with identical
DIMMs for best performance.
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Populate six identical memory modules per processor (one DIMM per channel) at a time to maximize performance.
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To ensure proper system cooling, memory module blanks must be installed in memory sockets that are not occupied.
DIMM population update for Performance Optimized mode with quantity of 4 and 8 DIMMs per processor.
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When the DIMM quantity is 4 per processor, the population is slot 1, 2, 4, 5.
NOTE:
For 2-1-1 platforms, full population with 8 DIMMs has no sequence concerns.
Mode-specific guidelines
Six memory channels are allocated to each processor. The allowable configurations depend on the memory mode selected.
Memory optimized (independent channel) mode
This mode supports Single Device Data Correction (SDDC) only for memory modules that use x4 device width. It does not impose any
specific slot population requirements.
Memory sparing
NOTE:
To use memory sparing, this feature must be enabled in System Setup.
In this mode, one rank per channel is reserved as a spare. If persistent correctable errors are detected on a rank, the data from this rank is
copied to the spare rank, and the failed rank is disabled.
With memory sparing enabled, the system memory available to the operating system is reduced by one rank per channel. For example, in a
dual-processor configuration with sixteen 4 GB single-rank memory modules, the available system memory is: 3/4 (ranks/channel) × 16
(memory modules) × 4 GB = 48 GB, and not 16 (memory modules) × 4 GB = 64 GB.
NOTE:
Memory sparing does not offer protection against a multi-bit uncorrectable error.
NOTE:
Both Advanced ECC/Lockstep and Optimizer modes support memory sparing.
Memory mirroring
Memory mirroring offers the strongest memory module reliability mode compared to all other modes, providing improved uncorrectable
multi-bit failure protection. In a mirrored configuration, the total available system memory is one half of the total installed physical memory.
Half of the installed memory is used to mirror the active memory modules. In the event of an uncorrectable error, the system switches over
to the mirrored copy. This ensures SDDC and multi-bit protection.
The installation guidelines for memory modules are as follows:
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Memory modules must be identical in size, speed, and technology.
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Installing and removing server components
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