Memory mirroringMemory-mirroring mode replicates and stores data on two pairs of DIMMs withintwo channels simultaneously. If a failure occurs, the memory controller switchesfrom the primary pair of memory DIMMs to the backup pair of DIMMs.To enable memory mirroring through the Setup utility, select System Settings >Memory. For more information, see “Using the Setup utility” on page 112. Whenyou use the memory mirroring feature, consider the following information:v When you use memory mirroring, you must install a pair of DIMMs at a time.One DIMM must be in channel 0, and the mirroring DIMM must be in the sameslot in channel 1. The two DIMMs in each pair must be identical in size, type,and rank (single or dual), and organization, but not in speed. The channels runat the speed of the slowest DIMM in any of the channels.v Channel 2, DIMM connectors 7, 8, 9, 16, 17, and 18 are not used inmemory-mirroring mode.v The maximum available memory is reduced to half of the installed memorywhen memory mirroring is enabled. For example, if you install 64 GB ofmemory using RDIMMs, only 32 GB of addressable memory is available whenyou use memory mirroring.The following diagram shows the memory channel interface layout with theDIMM installation sequence for mirroring mode. The numbers within the boxesindicate the DIMM population sequence in pairs within the channels, and thenumbers next to the boxes indicate the DIMM connectors within the channels. Forexample, the following illustration shows the first pair of DIMMs (indicated byones (1) inside the boxes) should be installed in DIMM connectors 1 on channel 0and DIMM connector 2 on channel 1. DIMM connectors 3, 6, 9, 12, 15, and 18 onchannel 2 are not used in memory-mirroring mode.The following table lists the DIMM connectors on each memory channel.Table 11. Connectors on each memory channelMemory channel DIMM connectorChannel 0 1, 2, 3, 10, 11, 12Channel 1 4, 5, 6, 13, 14, 15Channel 2 7, 8, 9, 16, 17, 18CH0CH1CH2CPU1112233362 15 48 7CH2CH0CH14461210 1115161413QPI5569 1817CPU2Figure 30. Memory channel interface layout58 IBM System x3550 M3 Type 4254 and 7944: Installation and User's Guide
