Chapter 4. IBM System x3690 X5 141memory channels, with configurations balanced across the memory buffers, so thatHemisphere Mode is maintained.Figure 4-18 Relative memory performance using mixed DIMMsAs you can see, mixing DIMM sizes can cause performance loss up to 18%, even if allchannels are occupied and Hemisphere Mode is maintained.4.8.6 Memory mirroringMemory mirroring is supported using x3690 X5 and MAX5. The DIMMs must be installed insets of four. The DIMMs in each set must be the same size and type, which is applicable alsowhen the memory mezzanine is installed in the server and if a MAX5 memory expansion unitis attached to the server. You must install DIMMs in sets of four DIMMs for memory-mirroringmode in each server and memory tray and in the MAX5.The maximum available memory is reduced to half of the installed memory when memorymirroring is enabled. Partial mirroring (mirroring of part but not all of the installed memory) isnot supported. For a detailed understanding of memory mirroring, see “Memory mirroring” onpage 28.DIMM installation for 3690 X5Table 4-12 lists the DIMM installation sequence for memory-mirroring mode when one or twoprocessors are installed in the server and no memory mezzanine tray is installed in theserver.Intel Xeon 7500 processorDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMBuffer Buffer Buffer BufferMemorycontrollerMemorycontrollerIntel Xeon 7500 processorDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMBuffer Buffer Buffer BufferMemorycontrollerMemorycontrollerIntel Xeon 7500 processorDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMBuffer Buffer Buffer BufferMemorycontrollerMemorycontrollerIntel Xeon 7500 processorDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMDIMMBuffer Buffer Buffer BufferMemorycontrollerMemorycontrollerDIMM 2 GB DIMMDIMM 4 GB DIMMEmpty DIMM socketRelative performance: 100 Relative performance: 97Relative performance: 92 Relative performance: 82A BC D
