Symptoms

Issue The message "missing memory" may be displayed when viewing available memory inside operating systems on the PowerEdge server compared to the amount of physical memory installed.

Cause

N/A

Resolution

Solution This is likely due to UPI Prefetch and/or Sub NUMA Cluster being enabled. Thus, hardware does not need to be replaced. Note: Both items are found in F2 System Setup under Processor settings. UPI Prefetch: Enables you to get the memory read started early on the DDR bus. The Ultra Path Interconnect (UPI) Rx path spawns the speculative memory read to the Integrated Memory Controller (iMC) directly. This option is set to Enabled by default. This is a cache prefetching setting designed to boost execution performance. Instructions and data are pulled from original storage locations and stored in this prefetched cache. A small amount of RAM is required for prefetching. Sub NUMA Cluster: Enables or disables the Sub NUMA Cluster. This option is set to Disabled by default. This is an address-mapping mechanism designed to lower LLC and memory latency between memory controllers on processors. A small amount of RAM is required for this mapping. In-depth details may be read about in the document from Intel. Disabling these two items restores most of the missing memory, but possibly at the cost of performance.

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