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Installing System Components 129
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 A3 and A4 or sockets B3 and B4), 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 Processor 2
Available
Memory
Spared
Memory
DIMM
A1
DIMM
A2
DIMM
A3
DIMM
A4
DIMM
B1
DIMM
B2
DIMM
B3
DIMM
B4
1 CPU /
2 CPUs
1 CPU /
2 CPUs
512
MB
512
MB
512
MB
512
MB
512
MB
512
MB
512
MB
512
MB
1 GB /
2 GB
1 GB /
2 GB
1 GB 1 GB
1 GB 1 GB 1 GB 1 GB 1 GB 1 GB 2 GB /
4 GB
2 GB /
4 GB
2 GB 2 GB
2 GB 2 GB 1 GB 1 GB 1 GB 1 GB 4 GB /
8 GB
2 GB /
4 GB
2 GB 2 GB
2 GB 2 GB 2 GB 2 GB 2 GB 2 GB 4 GB /
8 GB
2 GB /
4 GB
4 GB 4 GB
4 GB 4 GB 4 GB 4 GB 4 GB 4 GB 8 GB /
16 GB
4 GB /
8 GB
Indicates a spared single-rank DIMM (512-MB, 1-GB, or 2-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.