Understanding Demand vs. Utilization Memory Metrics in VMware Aria Operations

Products

• VCF Operations

Issue/Introduction

• The Summary > Time Remaining tab for a compute cluster displays "Demand Memory," but the Metrics tab only shows "Utilization Memory (KB)."
• Users observe that "Utilization Memory" is higher than "Consumed Memory" or the usage reported within the Guest OS (e.g., Windows Task Manager).
• Clarification is needed on how Aria Operations determines these values and why they differ from hypervisor-level metrics.

Environment

VMware VCF Operations/Aria Operations 

Cause

The discrepancy is due to the calculation logic of the Memory|Utilization (KB) metric. Aria Operations uses "Utilization" to represent the overall footprint of a VM to provide accurate capacity planning and "Time Remaining" projections. This metric is a conservative estimate designed to ensure the VM has enough memory to run optimally without swapping.

Resolution

How Utilization Memory is Determined

The calculation for Memory|Utilization (KB) depends on the status of VMware Tools within the virtual machine:

• If VMware Tools is Running: Utilization (KB) = Guest Needed Memory + (Guest Page In Rate * Page Size) + Total Capacity - Guest Physically Free

  • Note: "Guest Needed Memory" includes a 5% buffer for spikes to prevent guest-level swapping. Virtual machine memory usage higher than guest os

• If VMware Tools is NOT Running: Utilization (KB) = Memory Consumed (KB)

  • Note: In this state, the system may also prefer the Non Zero Active metric for certain calculations. VM Memory Utilization (KB) Discrepancy

Demand vs. Utilization

In the Time Remaining and Capacity dashboards, "Demand" is the terminology used for the workload's requirement. For memory, this "Demand" is mapped to the Utilization metric rather than Consumed. This ensures that the capacity model accounts for the guest's actual needs (including its internal cache and buffers) rather than just what the ESXi host has allocated.

Recommendations

If you require memory monitoring that more closely aligns with the Guest OS view (such as Windows Task Manager or Linux top):

• Use the Guest|Used Memory (KB) metric.
• The Memory|Consumed (KB) metric should be used if you only wish to see the hypervisor's view of memory pages actively being updated.