Online-spare memory

The memory online-spare feature disables the failed memory from the system configuration and activates an online-spare DIMM to replace the failed active DIMM.

You can enable either online-spare memory or memory mirroring in the Setup utility (see Using the Setup utility). When you use the memory online-spare feature, consider the following information:

The memory online-spare feature is supported on server models with an Intel Xeon™ 5600 series microprocessor.
When you enable the memory online-spare feature, you must install three DIMMs per microprocessor at a time. The first DIMM must be in channel 0, the second DIMM in channel 1, and the third DIMM in channel 2. The DIMMs must be identical in size, type, rank, and organization, but not in speed. The channels run at the speed of the slowest DIMM in any of the channels.
The maximum available memory is reduced to 2/3 of the installed memory when memory online-spare mode is enabled. For example, if you install 72 GB of memory using RDIMMs, only 48 GB of addressable memory is available when you use memory online-spare.

The following table shows the installation sequence for installing DIMMs for each microprocessor in memory online-spare mode:

Table 1. Memory online-spare mode DIMM population sequence.
Installed Microprocessor	DIMM connector
Microprocessor 1	3, 6, 9
	3, 6, 9, 2, 5, 8
	3, 6, 9, 2, 5, 8, 1, 4, 7
Microprocessor 2	12, 15, 18,
	12, 15, 18, 11, 14, 17,
	12, 15, 18, 11, 14, 17, 10, 13, 16

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