PowerEdge: Operating Systems on PowerEdge Servers may display less memory available than what is physically installed

Summary: This article introduces the memory issue that the Operating System on the PowerEdge servers may display less memory available than what is physically installed.

This article applies to This article does not apply to This article is not tied to any specific product. Not all product versions are identified in this article.
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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 documentThis hyperlink is taking you to a website outside of Dell Technologies. from Intel.

 

Disabling these two items restores most of the missing memory, but possibly at the cost of performance.

 



 

Affected Products

Poweredge C4140, PowerEdge C6420, PowerEdge C6520, PowerEdge FC640, PowerEdge M640, PowerEdge M640 (for PE VRTX), PowerEdge MX740C, PowerEdge MX750c, PowerEdge MX840C, PowerEdge R350, PowerEdge R440, PowerEdge R450, PowerEdge R540, PowerEdge R550 , PowerEdge R640, PowerEdge R650, PowerEdge R650xs, PowerEdge R740, PowerEdge R740XD, PowerEdge R740XD2, PowerEdge R750, PowerEdge R750XA, PowerEdge R750xs, PowerEdge R7515, PowerEdge R7525, PowerEdge R840, PowerEdge R940, PowerEdge R940xa, PowerEdge T350, PowerEdge T440, PowerEdge T550, PowerEdge T640, PowerEdge XE2420, PowerEdge XE7420, PowerEdge XE7440 ...
Article Properties
Article Number: 000139282
Article Type: Solution
Last Modified: 15 Apr 2025
Version:  4
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