Dell PowerEdge R900 - Manual (Page 93)

Installing System Components 93
• Mirrored mode requires the same DIMM type across and up-and-down
channels.
• In Single Channel Mode, a DIMM must be populated in the Branch 0,
Channel A, DIMM 1 slot first, then you can populate the Channel A up to
all 8 DIMMs.
• For the Dual Channel Mode, the memory capacity upgrade path would be
to populate Branch 0 of Channel A and Channel B with the same DIMM
number and type, or Branch 1 of Channel C and Channel D with the same
DIMM number and type.
Non-Optimal Memory Configurations
System performance can be affected if your memory configuration does not
conform to the preceding installation guidelines. Your system may issue an
error message during startup stating that your memory configuration is non-
optimal.
The server will support a population of DIMMs with different speed ratings.
The overall system memory speed will be determined by the slowest DIMM
populated.
The server will support population of mixed memory suppliers, provided all
other rules above are followed.
Memory Sparing Support
The system supports memory sparing if eight identical memory modules are
installed in the system. The memory sparing feature must be enabled in the
System Setup program and can be used only if memory mirroring is not
enabled.
Memory sparing allocates four ranks of DIMM memory to the spare bank.
These four ranks consist of the first rank of memory in DIMM sockets 1
through 4. For single-rank DIMMs, the entire capacity of the four DIMMs is
allocated to sparing whereas for dual-rank DIMMs, only half of the four-
DIMM capacity is allocated to sparing. Table 3-1 shows how memory sparing
splits the available and spared memory in each of the single- and dual-ranked
memory module combinations.