RDIMM memory mirroring mode installation order

Memory-mirroring mode provides full memory redundancy while reducing the total system memory capacity in half. Memory channels are grouped in pairs with each channel receiving the same data. If a failure occurs, the memory controller switches from the DIMMs on the primary channel to the DIMMs on the backup channel. The DIMM installation order for memory mirroring varies based on the number of processors and DIMMs installed in the server.

Memory mirroring guidelines

Memory mirroring is supported between two memory controllers within a cluster.
Mirroring is only supported for adjacent IMC pairs (e.g., IMC 0 & 1, IMC 2 & 3, etc.). Mirroring is not supported for non-adjacent IMC pairs (e.g., IMC 1 & 2).
Mirroring is restricted to a pair of channels (i.e., two channels). Three-channel mirroring is not supported.
The BIOS must configure one IMC in the pair as the primary and the other as the secondary.
Mirroring is supported in 1LM mode.
Mirrored memory regions must have identical densities and capacities (i.e., same size and type).

With two processors

The following table shows the DIMM population sequence for memory mirroring mode when two processors are installed.

Table 1. Memory mirroring with two processors
Total DIMMs	Processor 1
Total DIMMs	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1
16 DIMMs	16		14		12		10			7		5		3		1
32 DIMMs	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1
Total DIMMs	Processor 2
Total DIMMs	32	31	30	29	28	27	26	25	24	23	22	21	20	19	18	17
16 DIMMs	32		30		28		26			23		21		19		17
32 DIMMs	32	31	30	29	28	27	26	25	24	23	22	21	20	19	18	17

Note

Supported DIMM capacities and types:
- 16 DIMMs: 64/96/128 GB RDIMMs or 256 GB 3DS RDIMMs
- 32 DIMMs: 64/96/128 GB RDIMMs or 256 GB 3DS RDIMMs
All DIMMs populated must be of the same type and the same capacity.
DIMM configurations that support the Sub NUMA Clustering (SNC) feature, which can be enabled via UEFI. SNC is not supported if DIMM population does not follow the sequence indicated by the table above.

With four processors

The following table shows the DIMM population sequence for memory mirroring mode when four processors are installed.

Table 2. Memory mirroring with four processors
Total DIMMs	Processor 1
Total DIMMs	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1
32 DIMMs	16		14		12		10			7		5		3		1
64 DIMMs	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1
Total DIMMs	Processor 2
Total DIMMs	32	31	30	29	28	27	26	25	24	23	22	21	20	19	18	17
32 DIMMs	32		30		28		26			23		21		19		17
64 DIMMs	32	31	30	29	28	27	26	25	24	23	22	21	20	19	18	17
Total DIMMs	Processor 3
Total DIMMs	33	34	35	36	37	38	39	40	41	42	43	44	45	46	47	48
32 DIMMs	33		35		37		39			42		44		46		48
64 DIMMs	33	34	35	36	37	38	39	40	41	42	43	44	45	46	47	48
Total DIMMs	Processor 4
Total DIMMs	49	50	51	52	53	54	55	56	57	58	59	60	61	62	63	64
32 DIMMs	49		51		53		55			58		60		62		64
64 DIMMs	49	50	51	52	53	54	55	56	57	58	59	60	61	62	63	64

Note

Supported DIMM capacities and types:
- 32 DIMMs: 32/64/96/128 GB RDIMMs or 256 GB 3DS RDIMMs
- 64 DIMMs: 32/64/96/128 GB RDIMMs or 256 GB 3DS RDIMMs
All DIMMs populated must be of the same type and the same capacity.
DIMM configurations that support the Sub NUMA Clustering (SNC) feature, which can be enabled via UEFI. SNC is not supported if DIMM population does not follow the sequence indicated by the table above.

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RDIMM memory mirroring mode installation order

Memory mirroring guidelines​

With two processors​

With four processors​

Memory mirroring guidelines

With two processors

With four processors