Memory Mirroring - IBM System x3850 X5 Implementation Manual

Relative performance: 100
A
Intel Xeon 7500 processor
Memory
controller
Buffer Buffer Buffer
DIMM DIMM DIMM DIMM DIMM DIMM
DIMM DIMM DIMM DIMM
DIMM DIMM
DIMM DIMM
Relative performance: 92
C
Intel Xeon 7500 processor
Memory
controller
Buffer Buffer Buffer
DIMM DIMM DIMM DIMM DIMM DIMM
DIMM DIMM DIMM DIMM
DIMM DIMM
Figure 3-20 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.

3.8.4 Memory mirroring

Memory mirroring is supported using x3850 X5 with or without the MAX5. To enable memory
mirroring, you must install DIMMs in sets of four, one pair in each memory card. All DIMMs in
each set must be the same size and type. Memory cards 1 and 2 mirror each other, cards 3
and 4 mirror each other, memory cards 5 and 6 mirror each other, and cards 7 and 8 mirror
each other.
For x3850 X5, you install the memory evenly across all memory cards and then work your
way to filling all eight memory cards for the best performance.
The source and destination cards that are used for memory mirroring are not selectable by
the user. For a detailed understanding of memory mirroring, see "Memory mirroring" on
page 28.
x3850 X5 memory mirroring
Table 3-17 on page 88 shows DIMM placements for each solution.
Relative performance: 97
B
Memory
controller
Buffer Buffer
DIMM DIMM DIMM DIMM
DIMM DIMM DIMM
DIMM DIMM
DIMM DIMM
Relative performance: 82
D
Memory
controller
Buffer Buffer
DIMM DIMM DIMM
DIMM DIMM DIMM
DIMM DIMM
Intel Xeon 7500 processor
Memory Memory
controller controller
Buffer Buffer Buffer
DIMM DIMM DIMM DIMM
DIMM DIMM DIMM
DIMM DIMM DIMM DIMM
DIMM DIMM DIMM DIMM
Intel Xeon 7500 processor
Memory Memory
controller controller
Buffer Buffer Buffer
DIMM
DIMM DIMM DIMM
DIMM DIMM DIMM DIMM
population order
Chapter 3. IBM System x3850 X5 and x3950 X5
2 GB DIMM
DIMM
4 GB DIMM
DIMM
Empty DIMM socket
87