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• When you use memory mirroring, you must install a pair of DIMMs at a time. One DIMM must be in
channel 0, and the mirroring DIMM must be in the same slot in channel 1. The two DIMMs in each pair
must be identical in size, type, and rank (single or dual), and organization, but not in speed. The channels
run at the speed of the slowest DIMM in any of the channels.
• Channel 2, DIMM connectors 7, 8, 9, 16, 17, and 18 are not used in memory-mirroring mode.
• The maximum available memory is reduced to half of the installed memory when memory mirroring is
enabled. For example, if you install 64 GB of memory using RDIMMs, only 32 GB of addressable memory
is available when you use memory mirroring.
The following diagram shows the memory channel interface layout with the DIMM installation sequence for
mirroring mode. The numbers within the boxes indicate the DIMM population sequence in pairs within the
channels, and the numbers next to the boxes indicate the DIMM connectors within the channels. For
example, the following illustration shows the first pair of DIMMs (indicated by ones (1) inside the boxes)
should be installed in DIMM connectors 1 on channel 0 and DIMM connector 2 on channel 1. DIMM
connectors 3, 6, 9, 12, 15, and 18 on channel 2 are not used in memory-mirroring mode.
1
2
3
CH0
3
2
1
CPU1
CH1
1
2
3
6
5
4
CH2
9
8
7
Figure 36. Memory channel interface layout
The following table lists the DIMM connectors on each memory channel.
Table 17. Connectors on each memory channel
Memory channel
Channel 0
Channel 1
Channel 2
The following illustration shows the memory connector layout that is associated with each microprocessor.
For example, DIMM connectors 10, 11, 12, 13, 14, 15, 16, 17, and 18 (DIMM connectors are shown
underneath the boxes) are associated with microprocessor 2 (CPU2) and DIMM connectors 1, 2, 3, 4, 5, 6, 7,
8, and 9 are associated with microprocessor 1 (CPU1). The numbers within the boxes indicate the installation
sequence of the DIMM pairs. For example, the first DIMM pair (indicated within the boxes by ones (1)) should
be installed in DIMM connectors 1 and 2, which is associated with microprocessor 1 (CPU1).
Note: You can install DIMMs for microprocessor 2 as soon as you install microprocessor 2; you do not have
to wait until all of the DIMM slots for microprocessor 1 are filled.
System x3550 M3Problem Determination and Service Guide
434
6
5
CH0
10
CPU2
QPI
5
6
CH1
13
CH2
16
4
11
12
4
14
15
17
18
DIMM connector
1, 2, 3, 10, 11, 12
4, 5, 6, 13, 14, 15
7, 8, 9, 16, 17, 18
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