Lenovo 6241, Installation And Service Manual

Page: 66 / 1990

Table 9. DIMM population sequence for independent memory mode (continued)
DIMM installation order
Independent mode with memory
mirroring disabled Independent mode with memory
mirroring enabled
19 DIMM connector 3
20 DIMM connector 12
21 DIMM connector 13
22 DIMM connector 22
23 DIMM connector 21
24 DIMM connector 18
Memory mirroring
Use this information for an overview of memory mirroring.
Memory-mirroring replicates and stores data on DIMMs across all four memory channels for the compute
book and DDR3 or DDR4 channels simultaneously. If a failure occurs, the memory controller switches from
the DIMMs on the primary channels to the DIMMs on the backup channels. To enable memory mirroring
through the Setup utility, select
System Settings → Memory → Memory Mode . For more information, see
“Using the Setup utility” on page 123. For more information and notes about installing DIMMs, see “Installing
a memory module” on page 46. For more information and the DIMM population sequence for memory
mirroring, see “Memory mirroring in independent memory mode” on page 54 and “Memory mirroring in
lockstep mode” on page 58.
Memory mirroring is supported in independent mode and lockstep mode.
When you use the memory mirroring feature, consider the following information:
• The server supports single-socket memory mirroring. The compute book memory channel 0 mirrors
memory channel 1, and memory channel 2 mirrors memory channel 3. This mirroring provides redundancy
in memory but reduces the total memory capacity in half.
• DIMMs must be installed in pairs for each compute book when using the memory mirroring feature.
• The DIMM population must be identical (size, organization, etc.) for memory channel 0 and memory
channel 1, and identical for memory channel 2 and memory channel 3.
• Memory mirroring reduces the maximum available memory by half of the installed memory. For example, if
the server has 64 GB of installed memory, only 32 GB of addressable memory is available when memory
mirroring is enabled.
Memory rank sparing
This information provides an overview for memory rank sparing.
The server supports memory rank sparing. Memory rank sparing reserves memory capacity for failover in the
event of a DIMM failure, and the reserved capacity is subtracted from the total available memory. Memory
sparing provides less redundancy than memory mirroring does. If a predetermined threshold of correctable
errors is reached, the contents of the failing DIMM are copied to the spare memory, and the failing DIMM or
rank is disabled.
To enable memory sparing through the Setup utility, select System Settings → Memory → Memory Mode .
For more information and notes about installing DIMMs, see “Installing a memory module” on page 46. For
more information and the DIMM population sequence for memory rank sparing, see “Memory rank sparing in
independent mode” on page 55 and “Memory rank sparing in lockstep mode” on page 59.
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System x3850 X6 and x3950 X6 Installation and Service Guide