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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.
43
Chapter 3. Planning
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