Memory Rank Sparing In Independent Mode - IBM System x3850 X6 Installation And Service Manual

Memory rank sparing in independent mode

This information covers using the memory rank sparing feature in independent
memory mode.
The server supports memory rank sparing. Memory rank sparing reserves memory
capacity for failover in the event of a DIMM failure, and the reserved capacity is
subtracted from the total available memory. Memory sparing provides less
redundancy than memory mirroring does. If a predetermined threshold of
correctable errors is reached, the contents of the failing DIMM are copied to the
spare memory, and the failing DIMM or rank is disabled.
The DIMM installation order for memory rank sparing follows the independent
mode (performance) or lockstep mode (RAS) installation order based on the mode
of operation selected.
To enable memory rank sparing through the Setup utility, select System Settings →
Memory → Memory Mode. For more information, see "Using the Setup utility" on
page 126. For more information and notes about installing DIMMs, see "Installing
a memory module" on page 47.
The DIMM installation order for memory rank sparing follows the independent
mode (performance) or lockstep mode (RAS) installation order based on the mode
of operation selected. For more information, see "Independent memory mode" on
page 55, and "Lockstep memory mode" on page 59.
Consider the following when using the memory rank sparing feature in
independent memory mode:
v Memory rank sparing is not supported if memory mirroring is enabled.
v The spare rank must have identical or larger memory capacity than all the other
v When single-rank DIMMs (that is, 4 GB and 8 GB) are used, a minimum of two
v When multi-rank DIMMs (that is, 16 GB, 32 GB, and 64 GB) are used, one
v The total memory available in the system is reduced by the amount of memory
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System x3850 X6 and x3950 X6 Types 3837 and 3839: Installation and Service Guide
ranks on the same DDR3 channel.
rank DIMMs must be installed per memory channel to support memory sparing.
multi-rank DIMM can be installed per memory channel to support memory
sparing.
allocated for the spare ranks.