IBM 86884RX Installation Guide - Page 57

Key configuration rules relating to memory mirroring: Memory mirroring must be enabled in the System Setup (it is disabled by default). Enabling memory mirroring halves the amount of memory available to the operating system. You must install two pairs of DIMMs at a time. These four DIMMs (known as a bank) must be identical. Table 3-4 shows the pairs that are in each bank. Table 3-4 DIMMs that form a bank Bank DIMM pairs (see Table 3-3) 1 1 and 2 (DIMMs 1, 14, 15, 28) 2 3 and 4 (DIMMs 4, 11, 18, 25) 3 5 and 6 (DIMMs 2, 13, 16, 27) 4 7 and 8 (DIMMs 5, 10, 19, 24) 5 9 and 10 (DIMMs 3, 12, 17, 26) 6 11 and 12 (DIMMs 6, 9, 20, 23) 7 13 and 14 (DIMMs 7, 8, 21, 22) Note: The ability to hot-replace a failed DIMM or hot-add additional DIMMs is currently not supported. Memory performance considerations As shown in the server block diagram in Figure 1-1 on page 4, there are two memory ports to the memory controller, each with a throughput of up to 3.2 GBps. These ports correspond to the ports as shown in Figure 3-2 on page 42. The front side bus of the processors is 6.4 GBps, so maximum performance is achieved when both memory ports are used to access memory simultaneously. Consequently, for maximum performance, you must install four DIMMs of the same size at a time into a bank (see Table 3-4). In this configuration, all memory addresses are spread across all four DIMMs in the bank and, when accessed, both memory ports are used, resulting in 6.4 GBps burst transfer rates. Maximum performance can also be achieved with DIMMs of different sizes, as long as the total memory in port 1 matches the total memory in port 2. For example, if you have 6 DIMMs (four 512 MB DIMMs and two 1 GB DIMMs for a total of 4 GB), install all four 512 MB DIMMs (2 GB) in port 1 and the two 1 GB DIMMs (also 2 GB) in port 2. Chapter 3. Planning 43