Memory rank sparing in lockstep modeThis information covers using the memory rank sparing feature of the lockstepmemory mode.The server supports memory rank sparing. Memory rank sparing reserves memorycapacity for failover in the event of a DIMM failure, and the reserved capacity issubtracted from the total available memory. Memory sparing provides lessredundancy than memory mirroring does. If a predetermined threshold ofcorrectable errors is reached, the contents of the failing DIMM are copied to thespare memory, and the failing DIMM or rank is disabled.To enable memory sparing through the Setup utility, select System Settings →Memory → Memory Mode. For more information, see “Using the Setup utility” onpage 126. For more information and notes about installing DIMMs, see “Installinga memory module” on page 47The DIMM installation order for memory rank sparing follows the independentmode (performance) or lockstep mode (RAS) installation order based on the modeof operation selected. For more information, see “Independent memory mode” onpage 55, and “Lockstep memory mode” on page 59.Consider the following when using the memory rank sparing feature inindependent 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 otherranks on the same DDR3 channel.v When single-rank DIMMs (that is, 4 GB and 8 GB) are used, a minimum of tworank DIMMs must be installed per memory channel to support memory sparing.v When multi-rank DIMMs (that is, 16 GB, 32 GB, and 64 GB) are used, onemulti-rank DIMM can be installed per memory channel to support memorysparing.v The total memory available in the system is reduced by the amount of memoryallocated for the spare ranks.DIMM installation instructionsThis information provides instructions on how to install DIMMs formemory-mirroring mode.Note:v The information and installation procedures in this documentation apply to boththe 4-socket and the 8-socket configurations of the server, unless otherwisespecified. Most of the illustrations in the documentation show the 4-socketconfiguration of the server.v For additional information and notes that you need to consider when installingDIMMs, see “Installing a memory module” on page 47 and “Flash DIMMs” onpage 51.Attention: Static electricity that is released to internal server components when theserver is powered on might cause the server to stop, which might result in the lossof data. To avoid this potential problem, always use an electrostatic-discharge wriststrap and plug it into the electrostatic-discharge connector on the front of theserver (see “Front view of the server” on page 24 for the location of this connector)or other grounding system when you work inside the server with the power on.62 System x3850 X6 and x3950 X6 Types 3837 and 3839: Installation and Service Guide
