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. You must
enable memory mirroring through the Setup utility. For details about enabling
memory mirroring, see “Using the Setup utility” on page 99. When you use the
memory mirroring feature, consider the following information:
v DIMMs must be installed in pairs. The DIMMs in each pair must be the same
size and type.
v The maximum available memory is reduced to one third of the installed memory
when memory mirroring is enabled. For example, if you install 96 GB of memory,
only 32 GB of addressable memory is available when you use memory mirroring.
v Channel 1 DIMM connectors 1, 2, 7, and 8 are not used in memory-mirroring
mode.
The following table lists the installation sequence for installing DIMMs in
memory-mirroring mode.
Table 8. DIMM population sequence (memory-mirroring mode)
Number of Installed Microprocessors DIMM connector
13,5
4, 6
23,5
9, 11
4, 6
10, 12
Note: DIMM connectors 1, 2, 7, and 8 are not used in memory-mirroring
mode.
When you install or remove DIMMs, the server configuration information changes.
When you restart the server, the system displays a message that indicates that the
memory configuration has changed.
Rank sparing
When you use the memory mirroring feature, consider the following information:
v In rank sparing mode, one rank of a DIMM in each populated channel is reserved
as spare memory. The spare rank is not available as active memory. When the
active rank memory fails, its content is copied to the spare rank memory which
becomes active. The spare rank must have identical or larger memory capacity
than all the other ranks on the same channel.
v DIMMs must be installed in sets of three. The DIMMs in each set must be the
same size and type.
v The following table lists the DIMM installation sequence for rank sparing mode
when one or two microprocessors is installed in the server:
The following table shows the installation sequence for installing DIMMs for each
microprocessor in memory online-spare mode:
Chapter 2. Installing optional devices 75
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