Dell R805 manual Memory Sparing Support, Installing Memory Modules, Memory Sparing Configurations

8 GB	2 GB
12 GB	2 GB	1 GB
16 GB	2 GB	2 GB
24 GB	2 GB	2 GB	1 GB
32 GB	2 GB	2 GB	2 GB
16 GB	4 GB
24 GB	4 GB	2 GB
32 GB	4 GB	4 GB
48 GB	4 GB	4 GB	2 GB
64 GB	4 GB	4 GB	4 GB
32 GB	8 GB
48 GB	8 GB	4 GB
64 GB	8 GB	8 GB
96 GB	8 GB	8 GB	4 GB
128 GB	8 GB	8 GB	8 GB

Memory Sparing Support

Memory sparing is supported in systems that have one of the fully populated memory configurations shown in Table 3-1. The memory sparing feature must be enabled in the Memory Information screen of the System Setup program. See Using the System Setup Program.

NOTE: The Memory sparing and node interleaving features cannot be used at the same time. To use memory sparing, you must disable the Node Interleaving option in the System Setup program.

Memory sparing is applied independently to the two groups of DIMMs on opposite sides of the processor sockets. To support memory sparing, all DIMM sockets within a DIMM group must be populated.

When enabled, memory sparing allocates and reserves ranks of memory from the installed DIMMs to act as spare memory in the event of a memory channel failure. A memory channel uses paired DIMMs; for memory sparing to work, DIMMs must be paired as spares also.

Memory sparing allocates only the first rank of memory of a DIMM. For a single-rank DIMM, the entire capacity of the DIMM must be allocated for sparing along with the adjacent single-rank DIMM to spare a memory channel. For dual-rank DIMMs, two DIMMs are also required for sparing, but as only the first rank of each DIMM is allocated, only half of a dual-rank DIMM's capacity is allocated for sparing. The second ranks on both DIMMs are available memory.

Memory sparing calculates the appropriate DIMMs to spare by searching the DIMM sockets, starting with the higher-numbered socket pair (specifically, sockets 3 and 4 or sockets 7 and 8), for an amount of memory large enough to spare one of the available channels of memory. If the DIMMs in these sockets are sufficient to spare a channel of the available memory, the first rank of each of those two DIMMs are spared. If the amount of memory is not large enough to spare an available memory channel, the system spares the DIMM ranks in the lower-numbered sockets. Table 3-2 shows how memory sparing works in various memory configurations.

Table 3-2. Memory Sparing Configurations

		DIMMs
				Available Memory	Spared
A1, A2, B1, B2	A3, A4, B3, B4	A5, A6, B5, B6	A7, A8, B7, B8
					Memory
512 MB	512 MB	512 MB	512 MB	6 GB	2 GB
1 GB	1 GB	1 GB	1 GB	12 GB	4 GB
2 GB	2 GB	2 GB	2 GB	28 GB	4 GB
4 GB	4 GB	4 GB	4 GB	56 GB	8 GB
8 GB	8 GB	8 GB	8 GB	112 GB	16 GB
	Indicates a spared single-rank DIMM (512-MB or 1-GB). The entire capacity of this DIMM is reserved for sparing.
	Indicates a spared dual-rank DIMM (2-GB and higher). One-half of this DIMM's capacity is reserved for sparing.

Installing Memory Modules

CAUTION: Many repairs may only be done by a certified service technician. You should only perform troubleshooting and simple repairs as authorized in your product documentation, or as directed by the online or telephone service and support team. Damage due to servicing that is not authorized by Dell is not covered by your warranty. Read and follow the safety instructions that came with the product.

1.Turn off the system, including any attached peripherals, and disconnect the system from the electrical outlet.

2.Open the system. See Opening the System.

3.Remove the memory cooling shroud. See Removing the Memory Module Cooling Shrouds.