Dell PowerEdge 6850 - Manual (Page 66)

Spare Bank Support
If four identical single-rank memory modules are installed on a memory riser card, two of the four modules in the same rank can function as a spare bank if you
select the spare bank option using the System Setup program.
Memory RAID Support
The system supports memory Redundant Array of Independent DIMMs (RAID) if identical memory modules are installed in riser cards A, B, C, and D (all four
memory riser cards are required for memory RAID support). Memory RAID must be enabled in the System Setup program.
Memory Mirroring Support
The system supports memory mirroring if identical memory modules are installed in riser card A and B or in riser card C and D (riser cards A and B are a mirror
pair and riser cards C and D are a mirror pair). Mirroring must be enabled in the System Setup program.
Table 6 -2 and Table 6 -3 show examples of different memory configurations. Table 6 -3 lists the various allowable combinations of single- and dual-ranked
memory modules
Table 6-2. Sample Memory Configurations per Memory Riser Card
Table 6-3. Allowable Memory Module Configurations – Single-Ranked and
Dual-Ranked Memory Modules
NOTE: Spare bank is not support between memory riser cards.
NOTE: Spare bank is not supported if memory RAID is enabled.
NOTE: Spare bank is not supported if mirroring is enabled.
Total Memory DIMM_1A DIMM_1B DIMM_2A DIMM_2B
512 MB 256 MB 256 MB none none
1 GB 256 MB 256 MB 256 MB 256 MB
1 GB 512 MB 512 MB none none
2 GB 512 MB 512 MB 512 MB 512 MB
2 GB 1 GB 1 GB none none
3 GB 1 GB 1 GB 512 MB 512 MB
4 GB 1 GB 1 GB 1 GB 1 GB
6 GB 2 GB 2 GB 1 GB 1 GB
8 GB 2 GB 2 GB 2 GB 2 GB
DIMM_1A DIMM_1B DIMM_2A DIMM_2B
Single rank Single rank none none