VM Memory Usage % Discrepancies when compare to vCenter Performance Overview, Guest OS Task Manager, or Linux top command

Products

• VMware Aria Suite

Issue/Introduction

The VM Memory Usage % displayed in Aria Operations is higher or lower than the value shown in the VM Guest OS Task Manager.

In vCenter, you see the VM with X% memory utilization in Monitor > Performance > Overview page, but in Aria Operations, it is showing Y% for the Memory|Usage(%) metric (the value of Y can be higher or lower than the value of X).

Environment

Aria Operations 8.x

Cause

• The discrepancies are due to the different data collection methods used by each tool and their view of the memory.
  • vCenter is reporting VM memory usage from the hypervisor perspective based on the memory pages that the VM is actively updating according to the ESXi host every 20 seconds
  • The Guest OS Task Manager or the Linux top command reports memory usage from the OS perspective in real-time.
  • Aria Operations is collecting a number of the vCenter 20-second data samples every collection cycle (5 minutes by default) and averaging them.

 

Resolution

The Virtual Machine Memory Usage (%) metric is calculated using the following formula: VM Memory|Usage (%) = Guest|Needed Memory (KB) / Memory|Total Capacity (KB) * 100

Note: the Memory Usage metric seen in vSphere is different and corresponds with the "Memory|Consumed (%)" and "Memory|Balloon (KB)" in Aria Operations. Memory usage from Task Manager for Windows machines, and GiB Mem result from top command output for Linux machines are the ones closer to what's reported in Aria Operations. But there will still be discrepancies.

Additional Information

• For a closer comparison to the Guest OS measurements, refer to OS and Application Monitoring.
• It is recommended to maintain the default collection cycle of 5 minutes for Aria Operations metrics to balance data accuracy with performance considerations.
• Decreasing the collection interval may lead to excessive data collection, potentially impacting vRops storage and performance.

To learn more about vSphere metrics and VCF transformations, please see the downloadable ebook below from the Broadcom community forums.

vSphere Metrics, 4th edition

VCF Operations Transformation, 4th edition