v A minimum of two DIMMs must be installed in the memory expansion module
for each microprocessor in the host server.
v The maximum operating speed of the memory expansion module is determined
by the slowest DIMM installed in the memory expansion module.
v The memory expansion module does not come with any DIMMs installed when
you purchase it as a option. When you install DIMMs, install them in the order
shown in the following tables to optimize system performance.
v The server supports non-mirroring mode and memory-mirroring mode.
– Non-mirroring mode. When you use the non-mirroring mode, install DIMMs
as indicated in the following table.
Table 23. Non-mirroring mode DIMM population sequence for the memory expansion
module
Pairs of DIMMs DIMM connector population sequence
Pair 1 28, 29
Pair 2 9, 16
Pair 3 1, 8
Pair 4 20, 21
Pair 5 26, 31
Pair 6 11, 14
Pair 7 3, 6
Pair 8 18, 23
Pair 9 27, 30
Pair 10 10, 15
Pair 11 2, 7
Pair 12 19, 22
Pair 13 25, 32
Pair 14 12, 13
Pair 15 4, 5
Pair 16 17, 24
Note: When you populate DIMMs in the memory expansion module,
populate the larger capacity DIMMs first, then the smaller capacity DIMMs.
– Memory-mirroring mode. When you use the mirroring mode feature,
consider the following information:
- Memory-mirroring mode replicates and stores data on sets of four DIMMs
simultaneously. If a failure occurs, the memory controller switches from the
primary set of memory DIMMs to the backup set of DIMMs. To enable
memory mirroring through the Setup utility, select System Settings →
Memory. For more information, see “Configuring the server” on page 202.
- DIMMs must be installed in sets of four. The DIMMs in each set must be
the same size and type. This is applicable also when the memory expansion
module is attached to a host server and the host server has an optional
memory tray installed in the server. You must install DIMMs in sets of four
DIMMs for memory-mirroring mode in each (server, memory tray, and the
memory expansion module).
- The maximum available memory is reduced to half of the installed memory
when memory mirroring is enabled. For example, if the memory expansion
188 IBM System x3850 X5 and x3950 X5 Types 7145, 7146, 7143, and 7191: Problem Determination and Service Guide
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