Chapter 4. IBM System x3690 X5 141
memory channels, with configurations balanced across the memory buffers, so that
Hemisphere Mode is maintained.
Figure 4-18 Relative memory performance using mixed DIMMs
As you can see, mixing DIMM sizes can cause performance loss up to 18%, even if all
channels are occupied and Hemisphere Mode is maintained.
4.8.6 Memory mirroring
Memory mirroring is supported using x3690 X5 and MAX5. The DIMMs must be installed in
sets of four. The DIMMs in each set must be the same size and type, which is applicable also
when the memory mezzanine is installed in the server and if a MAX5 memory expansion unit
is attached to the server. You must install DIMMs in sets of four DIMMs for memory-mirroring
mode in each server and memory tray and in the MAX5.
The maximum available memory is reduced to half of the installed memory when memory
mirroring is enabled. Partial mirroring (mirroring of part but not all of the installed memory) is
not supported. For a detailed understanding of memory mirroring, see “Memory mirroring” on
page 28.
DIMM installation for 3690 X5
Table 4-12 lists the DIMM installation sequence for memory-mirroring mode when one or two
processors are installed in the server and no memory mezzanine tray is installed in the
server.
Intel Xeon 7500 processor
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMMDIMM
Buffer Buffer Buffer Buffer
Memory
controller
Memory
controller
Intel Xeon 7500 processor
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMMDIMM
Buffer Buffer Buffer Buffer
Memory
controller
Memory
controller
Intel Xeon 7500 processor
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMMDIMM
Buffer Buffer Buffer Buffer
Memory
controller
Memory
controller
Intel Xeon 7500 processor
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
Buffer Buffer Buffer Buffer
Memory
controller
Memory
controller
DIMM
2 GB DIMM
DIMM
4 GB DIMM
Empty DIMM socket
Relative performance: 100 Relative performance: 97
Relative performance: 92 Relative performance: 82
AB
C
D
142 IBM eX5 Implementation Guide
Table 4-13 shows the DIMM population order for memory-mirroring mode without the
mezzanine installed.
Table 4-12 Mirror DIMM installation: Two processors and no memory mezzanine installed
Table 4-13 DIMM population order: Memory-mirroring mode without the mezzanine installed
Table 4-14 lists the DIMM installation sequence for memory-mirroring mode when two
processors and a memory tray are installed in the server.
Table 4-14 Mirror DIMM installation: Two processors and memory mezzanine installed
Number of DIMMs
Processor 1 (planar DIMMs) Processor 2 (No mezzanine DIMMs)
Buffer Buffer Buffer Buffer Buffer Buffer Buffer Buffer
DIMM 1
DIMM 2
DIMM 3
DIMM 4
DIMM 5
DIMM 6
DIMM 7
DIMM 8
DIMM 9
DIMM 10
DIMM 11
DIMM 12
DIMM 13
DIMM 14
DIMM 15
DIMM 16
DIMM 17
DIMM 18
DIMM 19
DIMM 20
DIMM 21
DIMM 22
DIMM 23
DIMM 24
DIMM 25
DIMM 26
DIMM 27
DIMM 28
DIMM 29
DIMM 30
DIMM 31
DIMM 32
4 x x x x
8
x x x x x x x x
12
x x x x x x x x x x x x
16
x x x x x x x x x x x x x x x x
Sets of DIMMs Number of installed processors DIMM connector population sequence
with no memory tray
Set 1 1 or 2 1, 8, 9, 16
Set 2 1 or 2 3, 6, 11, 14
Set 3 1 or 2 2, 7, 10, 15
Set 4 1 or 2 4, 5, 12, 13
Number of DIMMs
Processor 1 (planar DIMMs) Processor 2 (with mezzanine DIMMs)
Buffer Buffer Buffer Buffer Buffer Buffer Buffer Buffer
DIMM 1
DIMM 2
DIMM 3
DIMM 4
DIMM 5
DIMM 6
DIMM 7
DIMM 8
DIMM 9
DIMM 10
DIMM 11
DIMM 12
DIMM 13
DIMM 14
DIMM 15
DIMM 16
DIMM 17
DIMM 18
DIMM 19
DIMM 20
DIMM 21
DIMM 22
DIMM 23
DIMM 24
DIMM 25
DIMM 26
DIMM 27
DIMM 28
DIMM 29
DIMM 30
DIMM 31
DIMM 32
8 x x x x x x x x
16
x x x x x x x x x x x x x x x x
24
x x x x x x x x x x x x x x x x x x x x x x x x
32
x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x

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