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Appendix B: Memory configuration options
172
Memory mirroring
Memory mirror requires either two or four same size memory boards
and provides redundancy at the cost of halving the effective memory
size. The memory configuration allows for the hot-replacement of an
existing board for a board containing an equal amount of memory or
the hot-addition of two memory boards to a pair of empty memory
board slots only.
A pair of memory boards in memory mirror mode forms a redundant
group. One of the memory boards is designated the primary image and
the other the secondary image. For memory writes, the write request is
issued to both boards. For memory reads, the read request is issued to
the primary memory board. In the event of a detected uncorrectable
error, the primary and secondary images switches with each other and
the failed image cannot become the primary image again until the
failed DIMMs have been replaced and the image re-built. The first
redundant group consists of memory board A mirrored with memory
board B. The second redundant group consists of memory board C
mirrored with memory board D. The BIOS sets the memory board
mirror LED to indicate that the memory board is operating in the
memoy mirror mode.
To configure memory mirroring:
1 Do either option below:
• Run BIOS setup. See “Entering BIOS setup” on page 96.
- or -
a During system bootup, enter the System Options Menu. See
“System options menu” on page 90.