‘Memory Reserved Not Equal to Allocated’ and ‘Insufficient CPU Reserved’ Alerts for Virtual Machines Restored from Backup

Products

• VMware vCenter Server

Issue/Introduction

After restoring Virtual Machines (VMs) from a backup solution, 3rd party monitoring applications may trigger critical alarms regarding resource reservations.

Users may observe the following errors:

• Error 1: Memory reserved on the virtual machine is not equal to its total allocated memory.
• Error 2: Insufficient CPU reserved for the Virtual Machine.
  

These alarms typically occur on real-time, high-performance applications (e.g., voice processing, databases) that require guaranteed physical hardware resources to maintain latency standards.

Environment

vCenter Server 8.0

Cause

When a Virtual Machine is restored from a backup, Resource Allocation settings including Shares, Limits, and Reservations are often reset to their default values (zero reservation).

This occurs because backup software cannot guarantee that the destination host or cluster has the same available unreserved capacity as the original source. For latency-sensitive applications, this lack of reservation triggers application-level alarms as the software detects it is running on "shared" rather than "guaranteed" resources.

Resolution

To resolve these alerts, the reservations must be manually re-applied.

Memory Reservation

1. Right-click the affected VM in the vSphere Client and select Edit Settings.
2. Expand the Memory section.
3. Locate the Reservation field.
4. Check the box labeled Reserve all guest memory (All locked).
• Note: If the box is already checked, uncheck it, click OK, then re-open settings and re-check it to force an API update to the .vmx configuration.
5. Click OK.
    

CPU Reservation

Since CPU does not have a "Reserve all" toggle, the value must be entered manually based on the host's physical clock speed.

1. Right-click the VM and select Edit Settings.
2. Expand the CPU section.
3. Locate the Reservation field (MHz).
4. Enter the required value (e.g., 19,200 MHz).
• Calculation: (Number of vCPUs) x (Clock Speed of Host Physical Core).
• Example: 8 vCPUs x 2400 MHz (2.4 GHz) = 19,200 MHz.
5. Click OK.

Note: While these changes can be applied while the VM is powered on, some applications may require a guest OS reboot to acknowledge the resource change and clear the alarm immediately