Configuring and using DDR3 memory with HP ProLiant Gen8 Servers

HP 1333 MT/s SmartMemory LRDIMMs are capable of operating at 1.35V at one and two DIMMs per channel and 1066

MT/s at three DIMMs per channel. Standard RDIMMs require 1.5V operation to maintain 1333 MT/s speed at one and two

DIMMs per channel. As Table 13 shows, using HP SmartMemory saves about 20% on power consumption while providing

the same performance as standard DIMMs in 2 DIMM per channel configurations.

Table 13. Lower power consumption with two 32 GB LRDIMMs per channel at 1.35V vs. 1.5V operation

2 DPC @ 1.5V 2DPC @ 1.35V Delta

Throughput (GB/s) 68.07 68.11 0%

Idle Power 38.4 35.32 9% lower

Loaded Power (W) 139.40 110.8 20% lower

Mixing DIMM sizes

There are no performance implications for mixing sets of different capacity DIMMs at the same operating speed. For

example, latency and throughput will not be negatively impacted by installing 8 x 4GB single-rank DDR3-1333 DIMMs

(one per channel), plus 8 x 8GB dual-rank DDR3-1333 DIMMs (one per channel).

General guidelines

For optimal throughput and latency, populate all four channels of each installed CPU identically.

Optimizing for lowest power consumption

Several factors determine the power that a DIMM consumes in a system. These include the DIMM technology used as

well as the DIMM’s capacity, its number of ranks, and its operating speed. Let’s take a quick look at each of these to see

how they affect power consumption.

DIMM types and power consumption

Because they do not use any buffering, UDIMMs are the lowest power consuming DIMM type. As Figure 11 shows, 4GB

UDIMMs consume about 35% less power than the comparable RDIMM. In general larger capacity DIMMs, which are

powering multiple ranks of DRAMs, consume more power. However, on a per gigabyte basis they are more efficient. A

32GB LRDIMM consumes 9 watts under load, but this is about one-half the power per GB of an 8 GB RDIMM.