Chapter 3. IBM System x3850 X5 and x3950 X5 87Figure 3-20 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.3.8.4 Memory mirroringMemory mirroring is supported using x3850 X5 with or without the MAX5. To enable memorymirroring, you must install DIMMs in sets of four, one pair in each memory card. All DIMMs ineach set must be the same size and type. Memory cards 1 and 2 mirror each other, cards 3and 4 mirror each other, memory cards 5 and 6 mirror each other, and cards 7 and 8 mirroreach other.For x3850 X5, you install the memory evenly across all memory cards and then work yourway to filling all eight memory cards for the best performance.The source and destination cards that are used for memory mirroring are not selectable bythe user. For a detailed understanding of memory mirroring, see “Memory mirroring” onpage 28.x3850 X5 memory mirroring population orderTable 3-17 on page 88 shows DIMM placements for each solution.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
