Memory Mirroring - IBM System x3550 M3 Type 4254 Installation And User Manual

the order shown in the following table to optimize system performance. In
non-mirroring mode, all three channels on the memory interface for each
microprocessor can be populated in any order and have no matching requirements.

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
more information, see "Using the Setup utility" on page 108. 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. Non-mirroring (normal) mode DIMM installation sequence
Installed microprocessors
Microprocessor socket 1
Microprocessor socket 2
One DIMM must be in channel 0, and the mirroring DIMM must be in the same
slot in channel 1. The two DIMMs in each pair must be identical in size, type,
and rank (single or dual) , and organization, but not in speed. The channels run
at the speed of the slowest DIMM in any of the channels.
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
3, 6, 9, 2, 5, 8, 1, 4, 7
12, 15, 18, 11, 14, 17, 10, 13, 16
3
CH0
1
CPU1 CPU2
QPI
3 CH1
4
CH2
7
6 5 4
CH0
10 11 12
6 5 4
CH1
13 14 15
CH2
17 18
16
Chapter 2. Installing optional devices
59