Lenovo System x3550 M4 Installation And Service Manual page 63

If a failure occurs, the memory controller switches from the primary pair of memory DIMMs to the backup
pair of DIMMs. To enable memory mirrored channel through the Setup utility, select System Settings ➙
Memory. For more information, see "Using the Setup utility" on page 97. When you use the memory
mirrored channel feature, consider the following information:
• When you use memory mirrored channel, you must install a pair of DIMMs at a time. The two DIMMs in
each pair must be identical in size, type, and rank (single, dual, or quad), and organization, but not in
speed. The channels run at the speed of the slowest DIMM in any of the channels.
• The maximum available memory is reduced to half of the installed memory when memory mirrored
channel 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 mirrored channel.
• For UDIMMs, DIMM connectors 3, 6, 7, and 10 for microprocessor 1 and DIMM connectors 15, 18, 19,
and 22 for microprocessor 2 are not used in memory mirrored channel mode.
The following diagram lists the DIMM connectors on each memory channel.
Figure 36. Connectors on each memory channel
The following table shows the installation sequence for memory mirrored channel mode:
Table 7. Memory mirrored channel mode DIMM population sequence
Number of DIMMs
First pair of DIMMs
Second pair of DIMMs
Third pair of DIMMs
Fourth pair of DIMMs
Fifth pair of DIMMs
Sixth pair of DIMMs
Seventh pair of DIMMs
Eighth pair of DIMMs
Ninth pair of DIMMs
Tenth pair of DIMMs
Eleventh pair of DIMMs
Twelfth pair of DIMMs
DIMM connectors 3, 6, 7, 10, 15, 18, 19, and 22 are not used in memory mirrored channel mode when UDIMMs
are installed in the server.
Number of installed
microprocessor
1
1
1
1
1
1
2
2
2
2
2
2
DIMM connector
1, 4
9, 12
2, 5
8, 11
3, 6
7, 10
13, 16
21, 24
14, 17
20, 23
15, 18
19, 22
.
Chapter 2 Installing optional devices
49