Dell R720XD owner manual Sample memory configurations, Memory Mirroring

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 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.

Sample memory configurations

The following tables show sample memory configurations for one and two processor configurations that follow the appropriate memory guidelines stated in this section.

NOTE: 16 GB quad-rank RDIMMs are not supported.

NOTE: 1R, 2R and 4R in the following tables indicate single-, dual-, and quad-rank DIMMs respectively.

Table 1. Memory configurations—single processor

System Capacity	DIMM Size (in	Number of	DIMM Rank, Organization,		DIMM Slot Population
(in GB)	GB)	DIMMs	and Frequency
2	2	1	1R, x8, 1333 MT/s,		A1
			1R, x8, 1600 MT/s
4	2	2	1R, x8, 1333 MT/s,		A1, A3
			1R, x8, 1600 MT/s
8	2	4	1R, x8, 1333 MT/s,		A1, A2, A3, A4
			1R, x8, 1600 MT/s
12	2	6	1R, x8, 1333 MT/s,		A1, A2, A3, A4, A5, A6
			1R, x8, 1600 MT/s
16	2	8	1R, x8, 1333 MT/s		A1, A2, A3, A4, A5, A6, A7, A8
	4	4	2R, x8, 1333 MT/s,		A1, A2, A3, A4
			2R, x8, 1600 MT/s
24	2	12	1R, x8, 1333	MT/s	A1, A2, A3, A4, A5, A6, A7, A8, A9, A10,
					A11, A12
	4	6	2R, x8, 1333	MT/s,	A1, A2, A3, A4, A5, A6
			2R, x8, 1600	MT/s
48	4	12	2R, x8, 1333	MT/s	A1, A2, A3, A4, A5, A6, A7, A8, A9, A10,
					A11, A12

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