Configuring and using DDR3 memory with HP ProLiant Gen8 Servers
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Figure 12. Power by memory speed using 8 x 8GB DIMMs installed at 1DIMM per channel.
General guidelines when optimizing for power consumption
When optimizing for lowest power consumption, you can use the following general rules.
• If you can meet your memory size requirements with them, use UDIMMs instead of RDIMMs. With their additional
memory channels, you can configure 2P ProLiant 24 slot Gen8 servers with as much as 128 GB using UDIMMs.
• Use the smallest number of DIMMs possible, by using the highest capacity DIMM available.
• For additional power savings with any memory configuration, you can run memory at the slowest speed possible.
With HP ProLiant Gen8 servers, this is 800 MT/s.
Optimizing for Resiliency
DDR3 DIMMs may be constructed using either 4-bit wide (x4) or 8-bit wide DRAM chips. Current ECC algorithms used in
the memory controllers are capable of detecting and correcting memory errors up to 4 bits wide. For DIMMS constructed
using x4 DRAMs, this means that an entire DRAM chip on the memory module can fail without causing a failure of the
module itself. DIMMs constructed using x8 DRAMs cannot tolerate the failure of DRAM chip. The ECC algorithm can
detect the failure, but it cannot correct it. As a result, systems configured with DIMMs using x4 DRAMs are safer from
potential memory failures than those using memory consisting of x8 DRAMs. While all UDIMMs are made with x8 DRAMs,
RDIMMs and LRDIMMs may be constructed with x4 or x8 DRAMs. To provide the highest levels of availability and
resiliency for ProLiant Gen8 servers, all HP SmartMemory RDIMMs and LRDIMMs use only x4 DRAMs.
You can increase the resiliency of servers with UDIMMs by selecting Lock-Step Mode through the ROM-based Setup
Utility (RBSU). This allows an entire x8 DRAM failure, but reduces the memory bandwidth of the server by 50%.
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8 GB 2R UDIMMs 1333 8 GB 2R RDIMMs 1333 8 GB 1R RDIMMs 1600
Total memory power consumption
8GB DIMMs installed at 1 DIMM per channel
Idle Power (W) Loaded Power (W)