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 reduces the maximum available memory by half of the installed memory. For example, if the server has 64 GB of installed memory, only 32 GB of addressable memory is available when memory mirroring is enabled.
Each DIMM must be identical in size and architecture.
DIMMs on each memory channel must be of equal density.
If two memory channels have DIMMs, mirroring occurs across two DIMMs (channels 0/1 will both contain the primary/secondary memory caches).
If three memory channels have DIMMs, mirroring occurs across all three DIMMs (channels 0/1, channels 1/2, and channels 2/0 will all contain primary/secondary memory caches).
Partial Memory Mirroring is a sub-function of memory mirroring. It requires following the memory installation order of memory mirroring mode.

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

With three processors

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

Table 2. Memory mirroring with three processors
Total DIMMs	Processor 1
Total DIMMs	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1
24 DIMMs	16		14		12		10			7		5		3		1
48 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
24 DIMMs	32		30		28		26			23		21		19		17
48 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
24 DIMMs	33		35		37		39			42		44		46		48
48 DIMMs	33	34	35	36	37	38	39	40	41	42	43	44	45	46	47	48

With four processors

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

Table 3. 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

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Memory mirroring mode installation order

With two processors​

With three processors​

With four processors​

With two processors

With three processors

With four processors