Cisco UCS C480 M5 Manual - Page 14

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DIMM Population Rules

When considering the memory configuration of your server, consider the following items:

Each channel has two DIMM slots (for example, channel A = slots A1 and A2).

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When both CPUs are installed, populate the DIMM slots of each CPU identically.

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For best memory performance, use identical DIMM types within a server (same speed, size

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and ranks).

For optimum performance, populate at least one DIMM per memory channel per CPU.

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When populating DIMM slots for optimal performance, multiples of 12 DIMMs are best

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because there are 6 memory channels per CPU socket and 2 CPUs must be populated.

For populations of 1 DIMM per channel (1DPC) and 2DPC, with Intel Xeon scalable processors,

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all supported DIMMs on Cisco UCS M5 servers run at their labeled speed provided the

processor supports that speed.

At the same memory speed, 2 DPC may perform slightly better than 1 DPC for RDIMMs

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(workload dependent).

For small to medium memory capacities, whenever possible, install dual rank RDIMMs for

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optimal performance. Dual rank RDIMMs perform slightly better than single rank RDIMMs.

Single rank DIMMs limit the performance of memory-intensive workloads in 1 DIMM per

channel configurations.

For applications requiring larger memory capacities, use 64 GB LRDIMMs or 64 GB TSV

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RDIMMs. At 1DPC, 64 GB LRDIMMs outperform 64 GB TSV DIMMs. However, at 2DPC the

performance of 64 GB LRDIMMs and 64 GB TSV RDIMMs is similar except for latency. At 2DPC,

64 GB TSV DIMMs have better latency than 64 GB LRDIMMs.

For applications requiring larger memory configuration, if there is a possibility of expanding

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the memory size in the future, use TSV RDIMMs. 64 GB TSV RDIMMs can be mixed with 128 GB

TSV DIMMs if needed.

128GB RDIMMs should be used for the largest memory capacity requirement (up to 3 TB for a

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2 socket server). These DIMMs provide the maximum memory size supported for 2 socket

UCS M5 servers based on Intel Xeon scalable processors.

A channel can operate with one or two DIMMs installed.

If a channel has only one DIMM, populate slot 1 first (the blue slot).

For 1, 2, 3, 4, and 6 DIMMs per socket configurations, fill the blue slots (slot 1) in the

memory channels as per recommended DIMM populations in

Order, page

16.

For 8 and 12 DIMMs per socket configurations, fill the blue slots (slot 1) and black

slots (slot 2) as per recommended DIMM populations in

page

16.

Refer to

DIMM Population Order, page 16

DIMM Population

DIMM Population Order,

for more details.

Cisco UCS C480 M5 Memory Guide