FB-DIMM : Performance Tuning , achieving maximum performance

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Performance tuning, achieving maximum performance

HP ProLiant servers implement a multi-branch memory architecture to reduce latency and enhance performance. This architecture allows the memory controller to fetch data in parallel from the different channels through memory interleaving. The latency for two channels is almost 40 percent lower than that of a single channel. The difference in latency between two channels and four channels is not as significant.

Figure 7 shows a dual-branch memory subsystem architecture using FB-DIMMs. To achieve maximum performance, all FB-DIMMs should be installed in matching sockets across each paired channel. For example, the FB-DIMM in slot 1A must be the same type (size and rank) as the FB-DIMM in slot 3A. Likewise, the FB-DIMMs in slots 2B and 4B must be the same type. While single- and dual-rank FB-DIMMs can be installed in a specific server, single-rank and dual-rank FB-DIMMs should not be mixed in matching dual-channel sockets.

General performance tuning tips include the use of dual-rank DIMMs and balanced channels. Use dual-rank DIMMs instead of single-rank DIMMs if possible. For example, using eight 1-GB DIMMs instead of sixteen 512MB DIMMs will improve performance. This has the added benefit of using less power per GB of memory. Also, when configuring memory, keep the channels balanced to minimize the latency per channel—latency increases with each additional set of FB-DIMMs.

Information provided by Hewlett-Packard Development Company, L.P.