IBM System x3850 X5 Implementation Guide

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

IBM System x3850 X5 Specifications

General

Brand	IBM
Model	System x3850 X5
Category	Server
Language	English