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Memory mirroring mode installation order
Memory-mirroring mode provides full memory redundancy while reducing the total system memory capacity
in half. Memory channels are grouped in pairs with each channel receiving the same data. If a failure occurs,
the memory controller switches from the DIMMs on the primary channel to the DIMMs on the backup
channel. The DIMM installation order for memory mirroring varies based on the number of processors and
DIMMs installed in the server.
Memory mirroring guidelines:
• Memory mirroring reduces the maximum available memory by half of the installed memory. For example, if
the server has 64 GB of installed memory, only 32 GB of addressable memory is available when memory
mirroring is enabled.
• Each DIMM must be identical in size and architecture.
• DIMMs on each memory channel must be of equal density.
• If two memory channels have DIMMs, mirroring occurs across two DIMMs (channels 0/1 will both contain
the primary/secondary memory caches).
• If three memory channels have DIMMs, mirroring occurs across all three DIMMs (channels 0/1, channels
1/2, and channels 2/0 will all contain primary/secondary memory caches).
• Partial Memory Mirroring is a sub-function of memory mirroring. It requires following the memory
installation order of memory mirroring mode.
With two processors
The following table shows the DIMM population sequence for memory mirroring mode when two processors
are installed.
Table 17. Memory mirroring with two processors
Total
DIMMs
16
15
16 DIMMs
16
32 DIMMs
16
15
Total
DIMMs
32
31
16 DIMMs
32
32 DIMMs
32
31
With three processors
The following table shows the DIMM population sequence for memory mirroring mode when three
processors are installed.
Table 18. Memory mirroring with three processors
Total
DIMMs
16
15
24 DIMMs
16
48 DIMMs
16
15
Total
DIMMs
32
31
14
13
12
11
10
14
12
10
14
13
12
11
10
30
29
28
27
26
30
28
26
30
29
28
27
26
14
13
12
11
10
14
12
10
14
13
12
11
10
30
29
28
27
26
Processor 1
9
8
7
6
7
9
8
7
6
Processor 2
25
24
23
22
23
25
24
23
22
Processor 1
9
8
7
6
7
9
8
7
6
Processor 2
25
24
23
22
.
Chapter 5
Hardware replacement procedures
5
4
3
2
5
3
5
4
3
2
21
20
19
18
21
19
21
20
19
18
5
4
3
2
5
3
5
4
3
2
21
20
19
18
1
1
1
17
17
17
1
1
1
17
53
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