With memory sparing enabled, the system memory available to the operating system is reduced by one
rank per channel. For example, in a dual-processor configuration with sixteen 4 GB dual-rank DIMMs, the
available system memory is: 3/4 (ranks/channel) × 16 (DIMMs) × 4 GB = 48 GB, and not 16 (DIMMs) × 4
GB = 64 GB.
NOTE: Memory sparing does not offer protection against a multi-bit uncorrectable error.
NOTE: Both Advanced ECC/Lockstep and Optimizer modes support Memory Sparing.

Memory Mirroring

Memory Mirroring offers the strongest DIMM reliability mode compared to all other modes, providing
improved uncorrectable multi-bit failure protection. In a mirrored configuration, the total available
system memory is one half of the total installed physical memory. Half of the installed memory is used to
mirror the active DIMMs. In the event of an uncorrectable error, the system will switch over to the
mirrored copy. This ensures SDDC and multi-bit protection.
Memory installation guidelines:
• Memory modules must be identical in size, speed, and technology.
• DIMMs installed in memory sockets with white release tabs must be identical and similar rule applies
for sockets with black and green release tabs. This ensures that identical DIMMs are installed in
matched pairs - for example, A1 with A2, A3 with A4, A5 with A6, and so on.

Sample Memory Configurations

The following tables show sample memory configurations that follow the appropriate memory guidelines
stated in this section.
NOTE: 1R, 2R, and 4R in the following tables indicate single-, dual-, and quad-rank DIMMs.
Table 3. Memory Configurations – Two Processors
System Capacity
(in GB) DIMM Size (in
GB) Number of
DIMMs Organization and
Speed DIMM Slot Population
4 2 2 1R x8, 1333 MT/s
1R x8, 1600 MT/s
A1, B1
8 2 4 1R x8, 1333 MT/s
1R x8, 1600 MT/s
A1, A2, B1, B2
16 2 8 1R x8, 1333 MT/s
1R x8, 1600 MT/s
A1, A2, A3, A4, B1, B2, B3,
B4
20 2 10 1R x8, 1333 MT/s
1R x8, 1600 MT/s
A1, A2, A3, A4, A5, B1, B2,
B3, B4, B5
32 2 16 1R x8, 1333 MT/s
1R x8, 1600 MT/s
A1, A2, A3, A4, A5, A6, A7,
A8, B1, B2, B3, B4, B5, B6,
B7, B8
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