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NOTE: You can mix x4 and x8 DRAM based DIMMs to support RAS features. However, all guidelines
for specific RAS features must be followed. x4 DRAM based DIMMs retain Single Device Data
Correction (SDDC) in memory optimized (independent channel) mode. x8 DRAM based DIMMs
require Advanced ECC mode to gain SDDC.
The following sections provide additional slot population guidelines for each mode:
Advanced ECC (lockstep)
Advanced ECC mode extends SDDC from x4 DRAM based DIMMs to both x4 and x8 DRAMs. This
protects against single DRAM chip failures during normal operation.
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.
NOTE: Advanced ECC with Mirroring is not supported.
Memory optimized (independent channel) mode
This mode supports SDDC only for memory modules that use x4 device width, and the mode does not
impose any specific slot population requirements.
Memory sparing
NOTE: To use memory sparing, this feature must be enabled in the System Setup.
In this mode, one rank per channel is reserved as a spare. If persistent correctable errors are detected on
a rank, the data from this rank is copied to the spare rank and the failed rank is disabled.
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 switches 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 levers 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.
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