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Memory Mirroring - IBM 7945G2U Installation And User Manual

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Memory mirroring

Memory-mirroring mode replicates and stores data on two pairs of DIMMs within
two channels simultaneously. If a failure occurs, the memory controller switches
from the primary pair of memory DIMMs to the backup pair of DIMMs. To enable
memory mirroring through the Setup utility, select System Settings → Memory. For
details about enabling memory mirroring, see "Using the Setup utility" on page 144.
When you use the memory mirroring feature, consider the following information:
v When you use memory mirroring, you must install a pair of DIMMs at a time.
v Channel 2, DIMM connectors 7, 8, 9, 16, 17, and 18 are not used in
v The maximum available memory is reduced to half of the installed memory when
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.
Figure 1. Memory channel interface layout
The following table lists the DIMM connectors on each memory channel.
Table 8. DIMM installation sequence for non-mirroring (normal) mode
Installed microprocessors
Microprocessor socket 1
Microprocessor socket 2
One DIMM must be in channel 0, and the mirroring DIMM must be in the same
connector in channel 1. The two DIMMs in each pair must be identical in size,
type, rank (single, dual, or quad), and organization. They do not have to be
identical in speed. The channels run at the speed of the slowest DIMM in any of
the channels. See Table 10 on page 109 for the DIMM connectors that are in
each pair.
memory-mirroring mode.
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.
1
2
3
2
1
2
6
5
9
8
DIMM connector population sequence
Install the DIMMs in the following sequence: 3, 6, 9, 2, 5, 8,
1, 4, 7
Install the DIMMs in the following sequence: 12, 15, 18, 11,
14, 17, 10, 13, 16
3
CH0
1
CPU1
CPU2
QPI
CH1
3
4
CH2
7
Chapter 2. Installing optional devices
6
5
4
CH0
10
11
12
6
5
4
CH1
13
14
15
CH2
16
17
18
107

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