Lenovo ThinkSystem SR950 Setup Manual page 104

Memory mirroring
Memory-mirroring mode provides full memory redundancy while reducing the total system memory capacity
in half. Memory channels are grouped in pairs with each channel receiving the same data. If a failure occurs,
the memory controller switches from the DIMMs on the primary channel to the DIMMs on the backup
channel. The DIMM installation order for memory mirroring varies based on the number of processors and
DIMMs installed in the server.
Memory mirroring guidelines:
• Memory mirroring reduces the maximum available memory by half of the installed memory. For example, if
the server has 64 GB of installed memory, only 32 GB of addressable memory is available when memory
mirroring is enabled.
• DIMMS are installed in pairs for each processor. Each DIMM in a pair must be identical in size and
architecture.
• DIMMs on each memory channel must be of equal density.
• If two memory channels have DIMMs, mirroring occurs across two DIMMs (channels 0/1 will both contain
the primary/secondary memory caches).
• If three memory channels have DIMMs, mirroring occurs across all three DIMMs (channels 0/1, channels
1/2, and channels 2/0 will all contain primary/secondary memory caches).
Figure 25. Processor and memory module layout
Memory mirroring DIMM population sequences for each of the supported processor configurations is shown
by one of the following topics:
• "Installation order: memory mirroring with two processors" on page 101
• "Installation order: memory mirroring with three processors" on page 102
• "Installation order: memory mirroring with four processors" on page 106
• "Installation order: memory mirroring with six processors" on page 110
• "Installation order: memory mirroring with eight processors" on page 122
For information about configuring memory settings, including how to enable memory mirroring, see "Memory
configuration" in the ThinkSystem SR950 Setup Guide.
ThinkSystem SR950 Setup Guide
100