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Memory guidelines

There are a number of criteria that must be followed when installing memory modules in your compute node.

Populating memory modules for best system performance

The DIMM (memory) population sequences in this document show all memory population combinations that are supported by your compute node. Some of these combinations will perform better than others because they balance the distribution of memory across processors, memory controllers, and memory channels. Balanced memory configurations enable optimal interleaving across all populated memory channels of a processor to boost memory performance. To populate balanced memory configurations for the best memory performance, observe the following guidelines:

  • When multiple processors are installed, balance the DIMMs across the processors so all processors have the same memory capacity.

  • Balance the DIMMs across the processor memory controllers so all memory controllers have exactly the same memory DIMM population and memory capacity. Each processor in your compute node has two memory controllers, each memory controller has three memory channels, and each memory channel has two DIMM slots.

  • Populate all memory channels for optimal performance.

  • For each memory controller, balance the DIMMs across all memory channels so all memory channels are configured with the same number of DIMMs, the same total memory capacity, and the same total number of memory ranks.

  • For memory configurations that do not require or allow use of all memory channels, all memory channels that are populated should have the same number of DIMMs, the same total memory capacity, and the same total number of memory ranks.

Where supported by specific memory population configurations, performance can be further enhanced by following these guidelines:

  • Select DIMMs by ranks for each populated memory channel, so the total number of ranks on each channel is an even number.

  • Select identical DIMMs to populate the DIMM slots for each populated memory channel when populating more than one DIMM slot per memory channel. For example, configure two identical 16 GB DIMMs on each populated memory channel. It is not required that the DIMMs on each memory channel be identical for the compute node to function, but memory performance will be slightly improved when using identical DIMMs.

Other rules when installing memory

When installing memory modules, observe the following criteria:

  • Install memory modules following only the sequences shown in Memory module installation order.

  • Do not mix RDIMMs and LR-DIMMs in the same compute node.

  • Install higher capacity (ranked) DIMMs first, following the specified population sequence.

  • Installing or removing DIMMs changes the compute node configuration. When you restart the compute node, it displays a message that indicates that the memory configuration has changed. To view the compute node configuration, use the Setup utility.