HP ProLiant DL360e Configuring and using DDR3 memory with HP ProLiant Gen8 Ser - Page 22

Understanding unbalanced memory configurations Unbalanced memory configurations are those in which the installed memory is not distributed evenly across the memory channels and/or the processors. ISS discourages unbalanced configurations because they will always have lower performance than similar balanced configurations. There are two types of unbalanced configurations, each with its own performance implications. • Unbalanced across channels. A memory configuration is unbalanced across channels if the memory capacities installed on each of the 4 channels of each installed processor are not identical. • Unbalanced across processors. A memory configuration is unbalanced across processors if a different amount of memory is installed on each of the processors. Memory configurations that are unbalanced across channels In unbalanced memory configurations across channels, the memory controller will split memory up into regions, as shown in Figure 12. Each region of memory will have different performance characteristics. The memory controller groups memory across channels as much as possible to create the regions. It will create as many regions as possible with DIMMs that span all four memory channels, since these have the highest performance. Next, it will move to create regions that span two memory channels and then to just one. Figure 12: A memory configuration that is unbalanced across memory channels The primary effect of memory configurations that are unbalanced across channels is a decrease in memory throughput in those regions that span fewer memory channels. In the example above, measured memory throughput in Region 2 may be as little as 25% of the throughput in Region 1. Memory configurations that are unbalanced across Processors Figure 13 shows a memory configuration that is unbalanced across processors. The CPU1 threads operating on the larger memory capacity of CPU1 may have adequate local memory with relatively low 22