Dell PowerEdge 2970 Hardware Owner's Manual page 93

When enabled, memory sparing allocates and reserves ranks of memory from the installed DIMMs to act
as spare memory in the event of a memory channel failure. A memory channel uses paired DIMMs; for
memory sparing to work, DIMMs must be paired as spares also.
Memory sparing allocates only the first rank of memory of a DIMM. For a single-rank DIMM, the entire
capacity of the DIMM must be allocated for sparing along with the adjacent single-rank DIMM to spare
a memory channel. For dual-rank DIMMs, two DIMMs are also required for sparing, but as only the first
rank of each DIMM is allocated, only half of a dual-rank DIMM's capacity is allocated for sparing. The
second ranks on both DIMMs are available memory.
Memory sparing calculates the appropriate DIMMs to spare by searching the DIMM sockets, starting
with the higher-numbered socket pair (specifically, sockets 3 and 4 or sockets 7 and 8), for an amount of
memory large enough to spare one of the available channels of memory. If the DIMMs in these sockets
are sufficient to spare a channel of the available memory, the first rank of each of those two DIMMs are
spared. If the amount of memory is not large enough to spare an available memory channel, the system
spares the DIMM ranks in the lower-numbered sockets. Table 3-2 shows how memory sparing works in
various memory configurations.
Table 3-2. Memory Sparing in Single- and Dual-Processor Configurations
Processor 1
DIMM 1 DIMM 2 DIMM 3
512 MB 512 MB 512 MB 512 MB
1 GB 1 GB 512 MB
1 GB 1 GB 1 GB
2 GB 2 GB 512 MB
2 GB 2 GB 1 GB
2 GB 2 GB 2 GB
4 GB 4 GB 512 MB
4 GB 4 GB 1 GB
4 GB 4 GB 2 GB
4 GB 4 GB 4 GB
*
8 GB 8 GB 1 GB
8 GB 8 GB 2 GB
8 GB 8 GB 4 GB
8 GB 8 GB 8 GB
Indicates a spared single-rank DIMM (512-MB or 1-GB). The entire capacity of this DIMM is reserved for sparing.
Indicates a spared dual-rank DIMM (2-GB and higher). One-half of this DIMM's capacity is reserved for sparing.
*
When available.
DIMM 4 DIMM 5 DIMM 6 DIMM 7
512 MB 512 MB
512 MB 1 GB 1 GB
1 GB 1 GB 1 GB
512 MB 2 GB 2 GB
1 GB 2 GB 2 GB
2 GB 2 GB 2 GB
512 MB 4 GB 4 GB
1 GB 4 GB 4 GB
2 GB 4 GB 4 GB
4 GB 4 GB 4 GB
1 GB 8 GB 8 GB
2 GB 8 GB 8 GB
4 GB 8 GB 8 GB
8 GB 8 GB 8 GB
Processor 2
DIMM8
512 MB 512 MB 1 GB / 2 GB
512 MB 512 MB
1 GB 1 GB
512 MB 512 MB
1 GB 1 GB
2 GB 2 GB
512 MB 512 MB
1 GB 1 GB
2 GB 2 GB
4 GB 4 GB
1 GB 1 GB
2 GB 2 GB
4 GB 4 GB
8 GB 8 GB
Installing System Components
Available Spared
Memory Memory
1 CPU / 2 CPUs 1 CPU / 2 CPUs
1 GB / 2 GB
1 GB / 2 GB 2 GB / 4 GB
2 GB / 4 GB 2 GB / 4 GB
3 GB / 6 GB 2 GB / 4 GB
4 GB / 8 GB 2 GB / 4 GB
6 GB / 12 GB 2 GB / 4 GB
5 GB / 10 GB 4 GB / 8 GB
6 GB / 12 GB 4 GB / 8 GB
8 GB / 16 GB 4 GB / 8 GB
12 GB / 24 GB 4 GB / 8 GB
10 GB / 20 GB 8 GB / 16 GB
12 GB / 24 GB 8 GB / 16 GB
16 GB / 32 GB 8 GB / 16 GB
24 GB / 48 GB 8 GB / 16 GB
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